Novel antimicrobial agents

ABSTRACT

A novel class of antimicrobial polymeric agents which are designed to exert antimicrobial activity while being stable, non-toxic and avoiding development of resistance thereto and a process of preparing same are disclosed. Further disclosed are pharmaceutical compositions containing same and a method of treating medical conditions associated with pathological microorganisms, a medical device, an imaging probe and a food preservative utilizing same. Further disclosed are conjugates of an amino acid residue and a hydrophobic moiety residue and a process of preparing same.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 11/500,461, filed Aug. 8, 2006, which is continuation in part of U.S. patent application Ser. No. 11/234,183, filed Sep. 26, 2005, now U.S. Pat. No. 7,504,381, issued on Mar. 17, 2009, which claims the benefit of priority from U.S. Provisional Patent Application No. 60/162,778, filed Sep. 27, 2004. The contents of the above applications are incorporated herein by reference in their entirety.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to novel antimicrobial agents and, more particularly, to a novel class of polymers which are designed to exert antimicrobial activity while being stable, non-toxic and avoiding development of resistance thereto. The present invention further relates to pharmaceutical compositions, medical devices and food preservatives containing such polymers and to methods of treating medical conditions associated with pathogenic microorganisms utilizing same.

Antibiotics, which are also referred to herein and in the art as antibacterial or antimicrobial agents, are natural substances of relatively small size in molecular terms, which are typically released by bacteria or fungi. These natural substances, as well as derivatives and/or modifications thereof, are used for many years as medications for treating infections caused by bacteria.

As early as 1928, Sir Alexander Fleming observed that colonies of the bacterium Staphylococcus aureus could be destroyed by the mold Penicillium notatum. His observations lead Fleming to postulate the existence and principle of action of antibiotic substances. It was established that the fungus releases the substance as a mean of inhibiting other organisms in a chemical warfare of microscopic scale. This principle was later utilized for developing medicaments that kill certain types of disease-causing bacteria inside the body. In 1940's Howard Florey and Ernst Chain isolated the active ingredient penicillin and developed a powdery form of the medicine.

These advancements had transformed medical care and dramatically reduced illness and death from infectious diseases. However, over the decades, almost all the prominent infection-causing bacterial strains have developed resistance to antibiotics.

Antibiotic resistance can result in severe adverse outcomes, such as increased mortality, morbidity and medical care costs for patients suffering from common infections, once easily treatable with antibiotics (Am. J. Infect. Control 24 (1996), 380-388; Am. J. Infect. Control 27 (1999), 520-532; Acar, J. F. (1997), Clin. Infect. Dis. 24, Suppl 1, S17-S18; Cohen, M. L. (1992), Science 257, 1050-1055; Cosgrove, S. E. and Carmeli, Y. (2003), Clin. Infect. Dis. 36, 1433-1437; Holmberg, S. D. et al. (1987), Rev. Infect. Dis. 9, 1065-1078) and therefore became one of the most recognized clinical problems of today's governmental, medicinal and pharmaceutical research (U.S. Congress, Office of Technology Assessment, Impacts of Antibiotic-Resistant Bacteria, OTA-H-629, Washington, D.C., U.S. Government Printing Office (1995); House of Lords, Science and Technology 7th Report: Resistance to Antibiotics and Other Antimicrobial Agents, HL Paper 81-II, session (1997-98); and Interagency Task Force on Antimicrobial Resistance, A Public Health Action Plan to Combat Antimicrobial Resistance. Part 1: Domestic issues).

Due to the limitations associated with the use of classical antibiotics, extensive studies have been focused on finding novel, efficient and non-resistance inducing antimicrobial/antibacterial agents.

Within these studies, a novel class of short, naturally occurring peptides, which exert outstanding antimicrobial/antibacterial activity, was uncovered.

These peptides, which are known as antimicrobial peptides (AMPs), are derived from animal sources and constitute a large and diverse family of peptides, which may serve as effective antimicrobial agents against antibiotic-resistant microorganisms (for recent reviews see, for example, Levy, O. (2000) Blood 96, 2564-2572; Mor, A. (2000) Drug Development Research 50, 440-447; Zasloff, M. (2002) New England Journal of Medicine 347, 1199-1200; Zasloff, M. (2002) Nature 415, 389-395; Zasloff, M. (2002) Lancet 360, 1116-1117). In the past 20 years, over 700 AMPs derived from various sources, from unicellular organisms to mammalians and including humans, have been identified (for recent reviews see, for example, Andreu, D. and Rivas, L. (1998) Biopolymers 47, 415-433; Boman, H. G. (2003) J. Intern. Med. 254, 197-215; Devine, D. A. and Hancock, R. E. (2002) Curr. Pharm. Des. 8, 703-714; Hancock, R. E. and Lehrer, R. (1998) Trends Biotechnol. 16, 82-88; Hancock, R. E. (2001) Lancet Infect. Dis. 1, 156-164; Hancock, R. E. and Rozek, A. (2002) FEMS Microbiol. Lett. 206, 143-149; Hoffmann, J. A. and Reichhart, J. M. (2002) Nat. Immunol. 3, 121-126; Lehrer, R. I. and Ganz, T. (1999) Curr. Opin. Immunol. 11, 23-27; Nicolas, P. and Mor, A. (1995) Annu. Rev. Microbiol. 49, 277-304; Nizet, V. and Gallo, R. L. (2002) Trends Microbiol. 10, 358-359; Shai, Y. (2002) Curr. Pharm. Des. 8, 715-725; Simmaco, M. et al. (1998) Biopolymers 47, 435-450; Tossi, A. et al. (2000) Biopolymers 55, 4-30; Tossi, A. and Sandri, L. (2002) Curr. Pharm. Des. 8, 743-761; Vizioli, J. and Salzet, M. (2002) Trends Pharmacol. Sci. 23, 494-496; Brogden, K. et al. (2003) Int. J. Antimicrob. Agents 22, 465-478 and Papagianni, M. (2003) Biotechnol. Adv. 21, 465-499).

AMPs are now recognized to have an important role in the innate host defense. They display a large heterogeneity in primary and secondary structures but share common features such as amphiphatic character and net positive charge. These features appear to form the basis for their cytolytic function. Ample data indicate that AMPs cause cells death by destabilizing the ordered structure of the cell membranes, although the detailed mechanism has not been fully understood yet (for recent reviews see, for example, Epand, R. M. et al. (1995), Biopolymers 37, 319-338; Epand, R. M. and Vogel, H. J. (1999), Biochim. Biophys. Acta 1462, 11-28; Gallo, R. L. and Huttner, K. M. (1998), J. Invest Dermatol. 111, 739-743; Gennaro, R. et al. (2002), Curr. Pharm. Des. 8, 763-778; Hansen, J. N. (1994), Crit. Rev. Food Sci. Nutr. 34, 69-93; Huang, H. W. (1999), Novartis. Found. Symp. 225, 188-200; Hwang, P. M. and Vogel, H. J. (1998), Biochem. Cell Biol. 76, 235-246; Lehrer, R. I. et al. (1993), Annu. Rev. Immunol. 11, 105-128; Matsuzaki, K. (1999), Biochim. Biophys. Acta 1462, 1-10; Muller, F. M. et al. (1999), Mycoses 42 Suppl 2, 77-82; Nissen-Meyer, J. and Nes, I. F. (1997), Arch. Microbiol. 167, 67-77; Peschel, A. (2002), Trends Microbiol. 10, 179-186; Sahl, H. G. and Bierbaum, G. (1998), Annu. Rev. Microbiol. 52, 41-79; Shai, Y. (1995), Trends Biochem. Sci. 20, 460-464; and Yeaman, M. R. and Yount, N.Y. (2003), Pharmacol. Rev. 55, 27-55). It is assumed that disturbance in membrane structure leads to leakage of small solutes (for example K⁺, amino acids and ATP) rapidly depleting the proton motive force, starving cells of energy and causing cessation of certain biosynthetic processes (Sahl, H. G. and Bierbaum, G. (1998), Annu. Rev. Microbiol. 52, 41-79). This mechanism is consistent with the hypothesis that antimicrobial activity is not mediated by interaction with a chiral center and may thus significantly prevent antibiotic-resistance by circumventing many of the mechanisms known to induce resistance.

In addition to their direct well-documented cytolytic (membrane-disrupting) activity, AMPs also display a variety of interesting biological activities in various antimicrobial fields. Some AMPs were shown to activate microbicidal activity in cells of the innate immunity including leukocytes and monocyte/macrophages (Ammar, B. et al. (1998), Biochem. Biophys. Res. Commun. 247, 870-875; Salzet, M. (2002) Trends Immunol. 23, 283-284; Scott, M. G. et al. (2000), J. Immunol. 165, 3358-3365; and Scott, M. G. et al. (2002), J. Immunol. 169, 3883-3891). Many cationic peptides are endowed with lipopolysaccharide binding activity, thus suppress the production of inflammatory cytokines and protect from the cascade of events that leads to endotoxic shock (Chapple, D. S. et al. (1998), Infect. Immun. 66, 2434-2440; Elsbach, P. and Weiss, J. (1998), Curr. Opin. Immunol. 10, 45-49; Lee, W. J. et al. (1998), Infect. Immun. 66, 1421-1426; Giacometti, A. et al. (2003), J. Chemother. 15, 129-133; Gough, M. et al. (1996), Infect. Immun. 64, 4922-4927; and Hancock, R. E. and Chapple, D. S. (1999), Antimicrob. Agents Chemother. 43, 1317-1323). Antimicrobial genes introduced into the genome of plants granted the plant the resistance to pathogens by expressing the peptide (Alan, A. R. et al. (2004), Plant Cell Rep. 22, 388-396; DeGray, G. et al. (2001), Plant Physiol 127, 852-862; Fritig, B., Heitz, T. and Legrand, M. (1998), Curr. Opin. Immunol. 10, 16-22; Osusky, M. et al. (2000), Nat. Biotechnol. 18, 1162-1166; Osusky, M. et al. (2004), Transgenic Res. 13, 181-190; and Powell, W. A. et al. (2000), Lett. Appl. Microbiol. 31, 163-168).

On top of the ribosomally synthesized antimicrobial peptides that have been identified and studied during the last 20 years, thousands of de-novo designed AMPs, were developed (Tossi, A. et al. (2000), Biopolymers 55, 4-30). These de-novo designed peptides are comprised of artificially designed sequences and were produced by genetic engineering or by chemical peptide syntheses. The finding that various antimicrobial peptides, having variable lengths and sequences, are all active at similar concentrations, has suggested a general mechanism for the anti-bacterial activity thereof rather than a specific mechanism that requires preferred active structures (Shai, Y. (2002), Biopolymers 66, 236-248). Naturally occurring peptides, and de-novo peptides having artificially designed sequences, either synthesized by humans or genetically engineered to be expressed in organisms, exhibit various levels of antibacterial and antifungal activity as well as lytic activity toward mammalian cells. As a result, AMPs are attractive targets for bio-mimicry and peptidomimetic development, as reproduction of critical peptide biophysical characteristics in an unnatural, sequence-specific oligomer should presumably be sufficient to endow antibacterial efficacy, while circumventing the limitations associated with peptide pharmaceuticals (Latham, P. W. (1999), Nat. Biotechnol. 17, 755-757).

One of the challenges in designing new antimicrobial peptides relies on developing peptidomimetics that would have high specificity toward bacterial or fungal cells, and consequently, would allow better understanding of the mechanism underlying the peptide lytic specificity, i.e., discrimination between cell membranes. Structure-activity relationships (SAR) studies on AMPs typically involve the systematic modification of naturally occurring molecules or the de-novo design of model peptidomimetics predicted to form amphiphatic alpha-helices or beta-sheets, and the determination of structure and activity via various approaches (Tossi, A. et al. (2000), Biopolymers 55, 4-30), as follows:

Minimalist methods for designing de-novo peptides are based on the requirement for an amphiphatic, alpha-helical or beta-sheet structure. The types of residues used are generally limited to the basic, positively charged amino acids lysine or arginine, and one to three of the hydrophobic residues alanine, leucine, isoleucine, glycine, valine, phenylalanine, or tryptophan (Blazyk, J. et al. (2001), J. Biol. Chem. 276, 27899-27906; Epand, R. F. et al. (2003), Biopolymers 71, 2-16; Hong, J. et al. (1999), Biochemistry 38, 16963-16973; Jing, W. et al. (2003), J. Pept. Res. 61, 219-229; Ono, S. et al. (1990), Biochim. Biophys. Acta 1022, 237-244; and Stark, M. et al. (2002), Antimicrob. Agents Chemother. 46, 3585-3590). While these approaches may lead to the design of potent antimicrobial agents, subtleties to the sequence of AMPs that may have been selected for by evolution are not considered and their absence may lead to a loss of specificity.

Sequence template methods for designing and synthesizing amphiphatic AMPs typically consists of extracting sequence patterns after comparison of a large series of natural counterparts. The advantage of this method, as compared with conventional sequence modification methods, is that it reduces the number of peptides that need to be synthesized in order to obtain useful results, while maintaining at least some of the sequence based information. As discussed hereinabove, the latter is lost in minimalist approaches (Tiozzo, E. et al. (1998), Biochem. Biophys. Res. Commun. 249, 202-206).

Sequence modification method includes all of the known and acceptable methods for modifying natural peptides, e.g., by removing, adding, or replacing one or more residues, truncating peptides at the N- or C-termini, or assembling chimeric peptides from segments of different natural peptides. These modifications have been extensively applied in the study of dermaseptins, cecropins, magainins, and melittins in particular (Scott, M. G. et al. (2000), J. Immunol. 165, 3358-3365; Balaban, N. et al. (2004), Antimicrob. Agents Chemother. 48, 2544-2550; Coote, P. J. et al. (1998), Antimicrob. Agents Chemother. 42, 2160-2170; Feder, R. et al. (2000), J. Biol. Chem. 275, 4230-4238; Gaidukov, L. et al. (2003), Biochemistry 42, 12866-12874; Kustanovich, I. et al. (2002), J. Biol. Chem. 277, 16941-16951; Mor, A. and Nicolas, P. (1994) J. Biol. Chem. 269, 1934-1939; Mor, A. et al. (1994), J. Biol. Chem. 269, 31635-31641; Oh, D. et al. (2000), Biochemistry 39, 11855-11864; Patrzykat, A. et al. (2002), Antimicrob. Agents Chemother. 46, 605-614; Piers, K. L. and Hancock, R. E. (1994) Mol. Microbiol. 12, 951-958; and Shepherd, C. M. et al. (2003), Biochemistry 370, 233-243).

The approaches described above have been applied in many studies aiming at designing novel AMPs. In these studies, the use of alpha-helix and/or beta-sheet inducing building blocks, the use of the more flexible beta-amino acid building blocks, the use of mixed D- and L-amino acid sequences and the use of facially amphiphilic arylamide polymers, have all demonstrated the importance of induced amphiphatic conformations on the biological activity of AMPs.

Antimicrobial peptides can act in synergy with classical antibiotics, probably by enabling access of antibiotics into the bacterial cell (Darveau, R. P. et al. (1991), Antimicrob. Agents Chemother. 35, 1153-1159; and Giacometti, A. et al. (2000), Diagn. Microbiol. Infect. Dis. 38, 115-118). Other potential uses include food preservation (Brul, S, and Coote, P. (1999), Int. J. Food Microbiol. 50, 1-17; Yaron, S., Rydlo, T. et al. (2003), Peptides 24, 1815-1821; Appendini, P. and Hotchkiss, J. H. (2000), J. Food Prot. 63, 889-893; and Johnsen, L. et al. (2000), Appl. Environ. Microbiol. 66, 4798-4802), imaging probes for detection of bacterial or fungal infection loci (Welling, M. M. et al. (2000), Eur. J. Nucl. Med. 27, 292-301; Knight, L. C. (2003), Q. J. Nucl. Med. 47, 279-291; and Lupetti, A. et al. (2003), Lancet Infect. Dis. 3, 223-229), antitumor activity (Baker, M. A. et al. (1993), Cancer Res. 53, 3052-3057; Jacob, L. and Zasloff, M. (1994), Ciba Found. Symp. 186, 197-216; Johnstone, S. A. et al. (2000), Anticancer Drug Des 15, 151-160; Moore, A. J. et al. (1994), Pept. Res. 7, 265-269; and Papo, N. and Shai, Y. (2003), Biochemistry 42, 9346-9354), mitogenic activity (Aarbiou, J. et al. (2002), J. Leukoc. Biol. 72, 167-174; Murphy, C. J. et al. (1993), J. Cell Physiol 155, 408-413; and Gudmundsson, G. H. and Agerberth, B. (1999), J. Immunol. Methods 232, 45-54) and lining of medical/surgical devices (Haynie, S. L. et al. (1995), Antimicrob. Agents Chemother. 39, 301-307).

However, while the potential of AMPs as new therapeutic agents is well recognized, the use of the presently known AMPs is limited by lack of adequate specificity, and optional systemic toxicity (House of Lords, Science and Technology 7th Report: Resistance to antibiotics and other antimicrobial agents. HL Paper 81-II, session, 1997-98; and Alan, A. R. et al. (2004), Plant Cell Rep. 22, 388-396). Thus, there is a clear need for developing new antimicrobial peptides with improved specificity and toxicity profile.

Moreover, although peptides are recognized as promising therapeutic and antimicrobial agents, their use is severely limited by their in vivo and ex vivo instability and by poor pharmacokinetics. Peptides and polypeptides are easily degraded in oxidative and acidic environments and therefore typically require intravenous administration (so as to avoid, e.g., degradation in the gastrointestinal tract). Peptides are further broken down in the blood system by proteolytic enzymes and are rapidly cleared from the circulation. Moreover, peptides are typically characterized by poor absorption after oral ingestion, in particular due to their relatively high molecular mass and/or the lack of specific transport systems. Furthermore, peptides are characterized by high solubility and therefore fail to cross biological barriers such as cell membranes and the blood brain barrier, but exhibit rapid excretion through the liver and kidneys. The therapeutic effect of peptides is further limited by the high flexibility thereof, which counteracts their receptor-affinity due to the steep entropy decrease upon binding and a considerable thermodynamic energy cost. In addition, peptides are heat and humidity sensitive and therefore their maintenance requires costly care, complex and inconvenient modes of administration, and high-cost of production and maintenance. The above disadvantages impede the use of peptides and polypeptides as efficient drugs and stimulate the quest for an alternative, which oftentimes involves peptidomimetic compounds.

Peptidomimetic compounds are modified polypeptides which are designed to have a superior stability, both in vivo and ex vivo, and yet at least the same receptor affinity, as compared with their parent peptides. In order to design efficacious peptidomimetics, an utmost detailed three-dimensional understanding of the interaction with the intended target is therefore required.

One method attempting at achieving the above goal utilizes synthetic combinatorial libraries (SCLs), a known powerful tool for rapidly obtaining optimized classes of active compounds. Thus, a number of novel antimicrobial compounds ranging from short peptides to small heterocyclic molecules have been identified from SCLs (Blondelle, S. E. and Lohner, K. (2000), Biopolymers 55, 74-87).

Several families of naturally occurring modified peptides which exhibit strong antimicrobial activity, have been uncovered in many organisms. These compounds, and their effective chemical alterations, have proposed a lead towards a general solution to the challenge of creating an antimicrobial compound devoid of the disadvantages associated with natural AMPs.

Thus, for example, naturally occurring short antimicrobial peptides characterized by a lipophilic acyl chain at the N-terminus were uncovered in various microorganisms (Bassarello, C. et al. (2004), J. Nat. Prod. 67, 811-816; Peggion, C., et al. (2003), J. Pept. Sci. 9, 679-689; and Toniolo, C. et al. (2001), Cell Mol. Life. Sci. 58, 1179-1188). Acylation of AMPs was hence largely used as a technique to endow AMPs with improved antimicrobial characteristics (Avrahami, D. et al. (2001), Biochemistry 40, 12591-12603; Avrahami, D. and Shai, Y. (2002), Biochemistry 41, 2254-2263; Chicharro, C. et al. (2001), Antimicrob. Agents Chemother. 45, 2441-2449; Chu-Kung, A. F. et al. (2004), Bioconjug. Chem. 15, 530-535; Efron, L. et al. (2002), J. Biol. Chem. 277, 24067-24072; Lockwood, N. A. et al. (2004), Biochem. J. 378, 93-103; Mak, P. et al. (2003), Int. J. Antimicrob. Agents 21, 13-19; and Wakabayashi, H. et al. (1999), Antimicrob. Agents Chemother. 43, 1267-1269). However, some studies indicate that attaching a hydrocarbon chain to the peptide, results in only marginal increase in the affinity of the lipopeptide to the membrane (Epand, R. M. (1997), Biopolymers 43, 15-24).

One family of AMPs capable of alluding towards the main goal is the family of dermaseptins. Dermaseptins are peptides isolated from the skin of various tree frogs of the Phyllomedusa species (Brand, G. D. et al. (2002), J. Biol. Chem. 277, 49332-49340; Charpentier, S. et al. (1998), J. Biol. Chem. 273, 14690-14697; Mor, A. et al. (1991), Biochemistry 30, 8824-8830; Mor, A. et al. (1994), Biochemistry 33, 6642-6650; Mor, A. and Nicolas, P. (1994), Eur. J. Biochem. 219, 145-154; and Wechselberger, C. (1998), Biochim. Biophys. Acta 1388, 279-283). These are structurally and functionally related cationic peptides, typically having 24-34 amino acid residues. Dermaseptins were found to exert rapid cytolytic activity, from seconds to minutes, in vitro, against a variety of microorganisms including viruses, bacteria, protozoa, yeast and filamentous fungi (Coote, P. J. et al. (1998), Antimicrob. Agents Chemother. 42, 2160-2170; Mor, A. and Nicolas, P. (1994), J. Biol. Chem. 269, 1934-1939; Mor, A. et al. (1994), J. Biol. Chem. 269, 31635-31641; Mor, A. and Nicolas, P. (1994), Eur. J. Biochem. 219, 145-154; Belaid, A. et al. (2002), J. Med. Virol. 66, 229-234; De Lucca, A. J. et al. (1998), Med. Mycol. 36, 291-298; Hernandez, C. et al. (1992), Eur. J. Cell Biol. 59, 414-424; and Mor, A. et al. (1991), J. Mycol. Med. 1, 5-10) as well as relatively inaccessible pathogens such as intracellular parasites (Efron, L. et al. (2002), J. Biol. Chem. 277, 24067-24072; Dagan, A. et al. (2002), Antimicrob. Agents Chemother. 46, 1059-1066; Ghosh, J. K. et al. (1997), J. Biol. Chem. 272, 31609-31616; and Krugliak, M. et al. (2000), Antimicrob. Agents Chemother. 44, 2442-2451).

Since dermaseptins portray the biodiversity existing in a very large group of antimicrobial peptides in terms of structural and biological properties, they serve as a general model system for understanding the function(s) of cationic antimicrobial peptides.

The 28-residue peptide dermaseptin S4 is known to bind avidly to biological membranes and to exert rapid cytolytic activity against a variety of pathogens as well as against erythrocytes (Mor, A. et al. (1994), J. Biol. Chem. 269(50): 31635-41).

In a search for an active derivative (peptidomimetic) of S4, a 28-residue derivative in which the amino acid residues at the fourth and twentieth positions were replaced by lysine residues, known as K₄K₂₀—S4, and two short derivatives of 16 and 13 residues in which the amino acid residue at the fourth position was replaced by a lysine residue, known as K₄—S4(1-16) and K₄—S4(1-13), respectively, were prepared and tested for the inhibitory effect thereof (Feder, R. et al. (2000), J. Biol. Chem. 275, 4230-4238). The minimal inhibitory concentrations (MICS) of these derivatives for 90% of the 66 clinical isolates tested (i.e., MIC₉₀ for S. aureus, P. aeruginosa and E. coli), varied between 2 and 8 μg/ml for the various species, whereby the 13-mer derivative K₄—S4(1-13) was found to be significantly less hemolytic when incubated with human erythrocytes, as compared with similarly active derivatives of magainin and protegrin, two confirmed antimicrobial peptide families (Fahrner, R. L. et al. (1996), Chem. Biol. 3(7): 543-50; Zasloff, M. et al. (1988), Proc. Natl. Acad. Sci. U S A 85(3): 910-3; Yang L. et al. (2000), Biophys. J., 79 2002-2009). Additional studies further confirmed that short, lysine-enriched S4 derivatives, are promising anti-microbial agents by being characterized by reduced toxicity and by showing efficacy also after pre-exposure of the subjects thereto.

N-terminal acylation of the C-terminally truncated 13-mer S4 derivative K₄—S4(1-13) also resulted in reduced hemolytic activity, whereby several derivatives, such as its aminoheptanoyl derivative, displayed potent and selective activity against the intracellular parasite, i.e., increased antiparasitic efficiency and reduced hemolysis. These studies indicate that increasing the hydrophobicity of anti-microbial peptides enhance their specificity, presumably by allowing such AMPs to act specifically on the membrane of intracellular parasites and thus support a proposed mechanism according to which the lipopeptide crosses the host cell plasma membrane and selectively disrupts the parasite membrane(s).

Overall, the data collected from in-vitro and in-vivo experiments indicated that some dermaseptin derivatives could be useful in the treatment of a variety of microbial-associated conditions including infections caused by multidrug-resistant pathogens. These agents were found highly efficacious, and no resistance was appeared to develop upon their administration. Nevertheless, the therapeutic use of these agents is still limited by the in vivo and ex vivo instability thereof, by poor pharmacokinetics, and by other disadvantageous characteristics of peptides, as discussed hereinabove.

In conclusion, most of the presently known antimicrobial peptides and peptidomimetics are of limited utility as therapeutic agents despite their promising antimicrobial activity. The need for compounds which have AMP characteristics, and are devoid of the limitations associated with AMPs is still present, and the concept of providing chemically and metabolically-stable active compounds in order to achieve enhanced specificity and hence enhanced clinical selectivity has been widely recognized.

There is thus a widely recognized need for, and it would be highly advantageous to have, novel, metabolically-stable, non-toxic and cost-effective antimicrobial agents devoid of the above limitations.

SUMMARY OF THE INVENTION

The present inventors have now designed and successfully prepared a novel class of polymeric compounds, which are based on positively charged amino acid residues and hydrophobic moieties. These novel polymers were found highly efficient as selective antimicrobial agents, while being devoid of toxicity and resistance induction.

Thus, according to one aspect of the present invention there is provided a polymer which includes two or more amino acid residues and one or more hydrophobic moiety residues, wherein one or more of the hydrophobic moiety residues is being covalently linked to at least two amino acid residues via the N-alpha of one amino acid residue and via the C-alpha of another amino acid residue.

According to further features in preferred embodiments of the invention described below, the polymer is having an antimicrobial activity.

According to still further features in the described preferred embodiments the polymer is capable of selectively destructing at least a portion of the cells of a pathogenic microorganism.

According to still further features in the described preferred embodiments the pathogenic microorganism is selected from the group consisting of a prokaryotic organism, an eubacterium, an archaebacterium, a eukaryotic organism, a yeast, a fungus, an alga, a protozon and a parasite.

According to still further features in the described preferred embodiments the polymer includes at least two hydrophobic moiety residues, wherein one or more of the hydrophobic moiety residues are linked to the N-alpha of an amino acid residue at the N-terminus of one of the amino acid residues and/or the C-alpha of another amino acid residue at the C-terminus.

According to still further features in the described preferred embodiments the polymer includes two or more hydrophobic moiety residues, wherein one or more of the hydrophobic moiety residues are linked to the side-chain of an amino acid residue in the polymer.

According to still further features in the described preferred embodiments one or more of the amino acid residues is a positively charged amino acid residue.

According to still further features in the described preferred embodiments the positively charged amino acid residue is selected from the group consisting of a histidine residue, a lysine residue, an ornithine residue and an arginine residue.

According to yet further features of the present invention, one or more of the hydrophobic moiety residues is linked to one or more of the amino acid residues via a peptide bond.

According to still further features in the described preferred embodiments one or more of the hydrophobic moiety residues is linked to two amino acid residues via a peptide bond.

According to still further features in the described preferred embodiments one or more of the hydrophobic moiety residues is linked to each of the amino acid residues via a peptide bond.

According to still further features in the described preferred embodiments one or more of the hydrophobic moiety residues is linked to the N-alpha of the amino acid residue via a peptide bond.

According to still further features in the described preferred embodiments one or more of the hydrophobic moiety residues is linked to the C-alpha of the amino acid residue via a peptide bond.

According to still further features in the described preferred embodiments one or more of the hydrophobic moieties has a carboxylic group at one end thereof and an amine group at the other end thereof.

According to still further features in the described preferred embodiments the polymer includes from 2 to 50 amino acid residues, preferably from 2 to 12 amino acid residues and more preferably from 2 to 8 amino acid residues.

According to still further features in the described preferred embodiments the polymer includes from 1 to 50 hydrophobic moiety residues, preferably from 1 to 12 hydrophobic moiety residues and more preferably from 1 to 8 hydrophobic moiety residues.

According to still further features in the described preferred embodiments the hydrophobic moiety residue includes one or more hydrocarbon chains which have from 4 to 30 carbon atoms.

According to still further features in the described preferred embodiments the hydrophobic moiety residue includes one or more fatty acid residues which are selected from the group consisting of an unbranched saturated fatty acid residue, a branched saturated fatty acid residue, an unbranched unsaturated fatty acid residue, a branched unsaturated fatty acid residue and any combination thereof, and the fatty acid residue has from 4 to 30 carbon atoms.

According to still further features in the described preferred embodiments the fatty acid residue is selected from the group consisting of a butyric acid residue, a caprylic acid residue and a lauric acid residue.

According to still further features in the described preferred embodiments one or more of the hydrophobic moieties is an ω-amino-fatty acid residue. The ω-amino-fatty acid residue is selected from the group consisting of 4-amino-butyric acid, 6-amino-caproic acid, 8-amino-caprylic acid, 10-amino-capric acid, 12-amino-lauric acid, 14-amino-myristic acid, 16-amino-palmitic acid, 18-amino-stearic acid, 18-amino-oleic acid, 16-amino-palmitoleic acid, 18-amino-linoleic acid, 18-amino-linolenic acid and 20-amino-arachidonic acid. Preferably, the ω-amino-fatty acid residue is selected from the group consisting of 4-amino-butyric acid, 8-amino-caprylic acid and 12-amino-lauric acid.

According to still further features in the described preferred embodiments all of the amino acid residues of the polymer are positively charged amino acid residues, such as lysine residues, histidine residues, ornithine residues, arginine residues and any combinations thereof.

According to still further features in the described preferred embodiments all the positively charged amino acid residues are lysine residues.

According to still further features of the preferred embodiments of the invention described below, the polymer further includes one or more active agent attached thereto.

According to still further features in the described preferred embodiments the active agent is attached to a side chain of an amino acid residue, either via the N-alpha of the amino acid residue at the N-terminus and/or the C-alpha of the amino acid residue at the C-terminus, and/or to one or more of the hydrophobic moiety residues of the polymer.

According to still further features in the described preferred embodiments the active agent is a labeling agent, which is selected from the group consisting of a fluorescent agent, a radioactive agent, a magnetic agent, a chromophore, a phosphorescent agent and a heavy metal cluster.

According to still further features in the described preferred embodiments the active agent comprises at least one therapeutically active agent, which is selected from the group consisting of an agonist residue, an amino acid residue, an analgesic residue, an antagonist residue, an antibiotic agent residue, an antibody residue, an antidepressant agent, an antigen residue, an anti-histamine residue, an anti-hypertensive agent, an anti-inflammatory drug residue, an anti-metabolic agent residue, an antimicrobial agent residue, an antioxidant residue, an anti-proliferative drug residue, an antisense residue, a chemotherapeutic drug residue, a co-factor residue, a cytokine residue, a drug residue, an enzyme residue, a growth factor residue, a heparin residue, a hormone residue, an immunoglobulin residue, an inhibitor residue, a ligand residue, a nucleic acid residue, an oligonucleotide residue, a peptide residue, a phospholipid residue, a prostaglandin residue, a protein residue, a toxin residue, a vitamin residue and any combination thereof.

According to still further features in the described preferred embodiments the polymer is capable of delivering one or more active agents, such as a labeling agent or a therapeutically active agent, to at least a portion of the cells of a pathogenic microorganism as described herein.

According to still further features in the described preferred embodiments the polymers are selected from the compounds presented in Table 3 hereinbelow.

According to still further features in the described preferred embodiments the polymer described herein can be represented by the general formula I:

X—W₀-[A₁-Z₁-D₁]-W₁-[A₂-Z₂-D₂]-W₂— . . . [An-Zn-Dn]-Wn-Y  Formula I

wherein:

n is an integer from 2 to 50, preferably from 2 to 12 and more preferably from 2 to 8;

A₁, A₂, . . . , An are each independently an amino acid residue, preferably a positively charged amino acid residue, and more preferably all of A₁, A₂, . . . , An are positively charged amino acid residues as discussed hereinabove, such as histidine residues, lysine residues, ornithine residues and arginine residues;

D₁, D₂, . . . , Dn are each independently a hydrophobic moiety residue, as described herein, or absent, provided that at least one such hydrophobic moiety residue exists in the polymer, and preferably at least one of the hydrophobic moiety residues is a ω-amino-fatty acid residue;

Z₁, Z₂, . . . Zn and W₀, W₁, W₂, . . . , Wn are each independently a linking moiety linking an amino acid residue and a hydrophobic moiety residue or absent, preferably at least one of the linking moieties is a peptide bond and most preferable all the linking moieties are peptide bonds;

X and Y may each independently be hydrogen, an amine, an amino acid residue, a hydrophobic moiety residue, another polymer having the general Formula I or absent.

According to still further features in the described preferred embodiments the polymer further includes one or more active agent, as described herein, attached to one or more of either X, Y, W₀, A₁, An and/or Wn.

According to another aspect of the present invention there is provided a conjugate which includes an amino acid residue and a hydrophobic moiety residue attached to the N-alpha or the C-alpha of the amino acid residue, the hydrophobic moiety residue being designed capable of forming a bond with an N-alpha or a C-alpha of an additional amino acid residue.

According to further features in the preferred embodiments of the invention described below, the hydrophobic moiety residue is attached to the N-alpha or the C-alpha of the amino acid residue via a peptide bond.

According to still further features in the described preferred embodiments the hydrophobic moiety has a carboxylic group at one end thereof and an amine group at the other end thereof and further includes a hydrocarbon chain as described herein.

According to still further features in the described preferred embodiments the hydrophobic moiety includes a fatty acid residue as described herein.

According to still further features in the described preferred embodiments the hydrophobic moiety is an ω-amino-fatty acid residue as described herein.

According to still another aspect of the present invention there is provided a process of preparing the conjugate described hereinabove, the process comprises providing an amino acid; providing a hydrophobic moiety having a first functional group that is capable of reacting with an N-alpha of an amino acid residue and/or a second functional group capable of reacting with a C-alpha of an amino acid; linking the first functional group in the hydrophobic moiety to the amino acid via the N-alpha of said amino acid; or linking the second functional group in the hydrophobic moiety to the amino acid via the C-alpha of the amino acid. Preferably the hydrophobic moiety is linked to the amino acid via a peptide bond.

According to further features in the preferred embodiments of the invention described below, the amino acid is a positively charged amino acid such as, for example, histidine, lysine, ornithine and arginine.

According to further features in the preferred embodiments all the positively charged amino acids are lysines.

According to still further features in the described preferred embodiments the hydrophobic moiety has a carboxylic group at one end thereof, an amine group at the other end thereof and a hydrocarbon chain, as described herein.

According to still further features in the described preferred embodiments the hydrophobic moiety includes a fatty acid residue as described herein.

According to still further features in the described preferred embodiments the hydrophobic moiety is an ω-amino-fatty acid residue as described herein.

According to still further features in the described preferred embodiments the hydrophobic moiety is a 8-amino-caprylic acid.

According to still further features in the described preferred embodiments, n is an integer from 6 to 8.

According to still further features in the described preferred embodiments, the polymer has the formula:

According to still further features in the described preferred embodiments, the polymer has the formula:

According to yet another aspect of the present invention there is provided a pharmaceutical composition which includes as an active ingredient the polymer of the present invention, described herein, and a pharmaceutically acceptable carrier.

According to further features in the preferred embodiments of the invention described below, the pharmaceutical composition is packaged in a packaging material and identified in print, in or on said packaging material, for use in the treatment of a medical condition associated with a pathogenic microorganism such as a prokaryotic organism, an eubacterium, an archaebacterium, a eukaryotic organism, a yeast, a fungus, an alga, a protozon and a parasite.

According to still further features in the described preferred embodiments the pharmaceutical composition further includes one or more additional therapeutically active agent as described herein, whereby preferably the therapeutically active agent includes an antibiotic agent.

According to another aspect of the present invention there is provided a method of treating a medical condition associated with a pathogenic microorganism, as described herein, the method includes administering to a subject in need thereof a therapeutically effective amount of the polymer described herein.

According to further features in the preferred embodiments of the invention described below, the administration is effected orally, rectally, intravenously, topically, intranasally, intradermally, transdermally, subcutaneously, intramuscularly, intraperitoneally or by intrathecal catheter.

According to still further features in the described preferred embodiments the method further includes administering to the subject one or more therapeutically active agent as described herein, preferably, an antibiotic agent.

According to still further features in the described preferred embodiments the polymer of the present invention is administered either per se or as a part of a pharmaceutical composition; the pharmaceutical composition further includes a pharmaceutically acceptable carrier, as described herein.

According to an additional aspect of the present invention there is provided a medical device which includes the polymer of the present invention and a delivery system configured for delivering the polymer to a bodily site of a subject.

According to further features in the preferred embodiments of the invention described below, the polymer forms a part of a pharmaceutical composition, and the pharmaceutical composition further includes a pharmaceutically acceptable carrier.

According to still further features in the described preferred embodiments the delivery is effected by inhalation, and the delivery system is selected from the group consisting of a metered dose inhaler, a respirator, a nebulizer inhaler, a dry powder inhaler, an electric warmer, a vaporizer, an atomizer and an aerosol generator.

According to still further features in the described preferred embodiments the delivery is effected transdermally, and the delivery system is selected from the group consisting of an adhesive plaster and a skin patch.

According to still further features in the described preferred embodiments the delivery is effected topically and the delivery system is selected from the group consisting of an adhesive strip, a bandage, an adhesive plaster, a wound dressing and a skin patch.

According to still further features in the described preferred embodiments the delivery is effected by implanting the medical device in a bodily organ. Preferably the delivery system further includes a biocompatible matrix which in turn includes a biodegradable polymer and further includes a slow release carrier.

According to still an additional aspect of the present invention there is provided a food preservative which includes an effective amount of the polymer of the present invention, and preferably further includes an edible carrier.

According to a further aspect of the present invention there is provided an imaging probe for detecting a pathogenic microorganism as described herein, which includes a polymer as described herein, and one or more labeling agent, as described herein, attached thereto.

According to further features in the preferred embodiments of the invention described below, the labeling agent(s) is attached to a side chain of an amino acid residue, a C-terminus and/or a N-terminus of the polymer and/or one of the hydrophobic residues of the polymer of the present invention.

The present invention successfully addresses the shortcomings of the presently known configurations by providing a novel class of antimicrobial polymers, which combine the merits of therapeutically active antimicrobial peptides, e.g., high efficacy and specificity, without exhibiting the disadvantages of peptides.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

The invention is herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

In the drawings:

FIG. 1 presents a cumulative bar graph demonstrating the high correlation between the antimicrobial activity and the hydrophobicity of exemplary polymers according to the present invention, by marking the polymers which exhibited a significant microbial activity (MIC value of less than 50 μM) against E. coli (in red bars), P. aeruginosa (in yellow bars), methicilin-resistant S. aureus (in blue bars) and B. cereus (in green bars), on the scale of the acetonitrile percentages in the mobile phase at which the polymers were eluted on a reverse phase HPLC column;

FIG. 2 presents a cumulative bar graph demonstrating the lack of correlation between the antimicrobial activity and the net positive charge of exemplary polymers according to the present invention, by marking the polymers which exhibited a significant microbial activity (MIC value of less than 50 μM) against E. coli (in red bars), P. aeruginosa (in yellow bars), methicilin-resistant S. aureus (in blue bars) and B. cereus (in green bars), over bins representing the net positive charge from +9 to +1;

FIGS. 3( a-c) presents a bar graph demonstrating the non-resistance inducing effect of exemplary polymers according to the present invention, by measuring MICs level evolution on E. coli after 10 iterations of successive exposures of bacteria to sub-lytic concentrations of K(NC₁₂K)₃NH₂ and C₁₂K(NC₈K)₅NH₂, as compared to exposures to three classical antibiotic agents, tetracycline, gentamycin and ciprofloxacin (FIG. 3 a), and on methicilin-resistant S. aureus after 15 iterations of successive exposures of bacteria to sub-lytic concentrations of C₁₂KKNC₁₂KNH₂, as compared to exposures to two antibiotic agents, rifampicin and tetracycline (FIG. 3 b), and the development of resistance of E. coli to C₁₂K(NC₈K)₇NH₂, evaluated during 15 serial passages, as compared to exposures to three classical antibiotic agents, ciprofloxacin, imipenem, and tetracycline (FIG. 3 c) (the relative MIC is the normalized ratio of the MIC obtained for a given subculture to the concomitantly determined MIC obtained on bacteria harvested from control wells (wells cultured without antimicrobial agent) from the previous generation;

FIG. 4 presents comparative plots demonstrating the kinetic bactericidal effect of C₁₂K(NC₈K)₅NH₂, an exemplary polymer according to the present invention, on E. coli. incubated in the presence of the polymer, with colony forming units (CFU) counts performed after the specified incubation periods and compared in a dose-dependent experiment at zero (control), 3 and 6 multiples of the minimal inhibitory concentration (MIC) value (3.1 μM) in LB medium at 37° C.;

FIG. 5 presents comparative plots demonstrating the kinetic bactericidal effect of C₁₂K(NC₈K)₇NH₂, an exemplary polymer according to the present invention (black triangles), on E. coli., compared with normal bacterial growth control (black circles), and with kinetic bactericidal effect of while Imipenem (white squares) and Ciprofloxacin (black squares), as determined at a concentration corresponding to six multiples of their respective MIC value (plotted values represent the mean±standard deviations obtained from at least two independent experiments);

FIG. 6 presents comparative plots demonstrating the hemolytic effect of C₁₂K(NC₈K)₇NH₂, an exemplary polymer according to the present invention, compared with the hemolytic effect of bivalirudin, a synthetic peptide and FDA approved thrombin inhibitor, and with the hemolytic effect of MSI-78, a magainin derivative, determined against human RBC (10% hematocrit) after 1 hour incubation at 37° C. in the presence of 31 μM (striped bars), 94 μM (gray bars) and 156 μM (white bars) polymer/peptide concentration (plotted values represent the mean±standard deviations obtained from at least four independent experiments);

FIG. 7 presents the circular dichroism spectra of two exemplary polymers according to the present invention, C₁₂K(NC₈K)₅NH₂ and C₁₂K(NC₈K)₇NH₂, taken in the designated media at polymer concentration of 100 μM (liposome concentration of 2 mM), expressed as mean residue molar ellipticity, and compared with a 15-residue control peptide, an acylated dermaseptin S4 derivative (data represent average values from three separate recordings);

FIG. 8 presents the circular dichroism spectra of C₁₂K(NC₈K)₇NH₂, another exemplary polymer according to the present invention (gray lines), and of a control antimicrobial peptide K₄S4(1-16) (black lines), taken in PBS alone (dashed lines) or in the presence of 2 mM POPC:POPG (3:1) liposomes concentration suspended in PBS (solid lines) (data represent average values from three separate recordings);

FIG. 9 presents association and dissociation curves (binding rates) obtained by surface plasmon resonance (SPR) measurements, demonstrating the membrane binding properties of various doses (0.21, 0.42, 0.84, 1.67, and 3.35 μg) of C₁₂K(NC₈K)₅NH₂, an exemplary polymer according to the present invention, to a model membrane (K_(app) is the resulting binding constants calculated assuming a 2-step model);

FIG. 10 presents a bar graph demonstrating the binding of exemplary polymers according to the present invention, denoted as KNC₈KNH₂, K(NC₈K)₂NH₂, K(NC₈K)₃NH₂, K(NC₈K)₆NH₂, KNC₁₂KNH₂, K(NC₁₂K)₂NH₂ and K(NC₁₂K)₃NH₂, to lipopolysaccharide, as measured by SPR, wherein the weaker binding of the polymers to liposomes after incubation with LPS substantiates that the polymers are bound to the LPS;

FIG. 11 presents a photograph of a UV illuminated 1% agarose gel electrophoresis, demonstrating the DNA binding characteristics of C₁₂KKNC₁₂KNH₂, K(NC₄K)₇NH₂ and C₁₂K(NC₈K)₅NH₂, exemplary polymers according to the present invention, as measured by DNA retardation assay after the polymers were incubated for 30 minutes at room temperature at the specified DNA/polymer ratios (w:w) using 200 nanograms of plasmid (normal migration in absence of the polymer of the plasmid pUC19 is shown in leftmost lane);

FIG. 12 presents comparative plots demonstrating the antimicrobial activity of C₈K(NC₈K)₇NH₂, an exemplary polymer according to the present invention (in black circles), against the micro-flora found in human saliva, as compared to 113-367, a peptide with known antimicrobial activity (in white circles) and the vehicle buffer as control (white triangle) in logarithmic units of CFU per ml versus incubation time;

FIG. 13 presents a comparative plot demonstrating the anti-malarial activity of C₁₂K(NC₁₂K)₃NH₂, an exemplary polymer according to the present invention, by showing the effect of time of exposure of the malaria causing parasites to the polymer on the stage-dependent effect on Plasmodium falciparum parasite viability (chloroquine-resistant FCR3 strain versus chloroquine-sensitive NF54 strain);

FIG. 14 presents a comparative plot demonstrating the anti-malarial activity of C₁₂KNC₈KNH₂, an exemplary polymer according to the present invention, by showing the effect of time of treatment at different parasite developmental stages with the polymer, on parasite viability;

FIGS. 15 a-b present the rate of survival, monitored over time period of 7 days, of infected mice (n=10 per group) inoculated intraperitoneally with 2.5×10⁶ CFUs of E. coli CI-3504 (FIG. 15 a) and 5×10⁶ CFUs of E. coli (FIG. 15 b), and subsequently treated intraperitoneally with PBS (black circles), with a single dose of 4 mg/kg C₁₂K(NC₈K)₇NH₂ (gray squares) or with four doses of 2 mg/kg Imipenem (asterisk), demonstrating the high in-vivo efficacy of the polymers of the present invention; and

FIG. 16 presents the rate of survival, monitored over time period of 6 days, of mice (n=12 per group) treated intraperitoneally with a blank control (white bars), 4 mg/kg body weight (sparsely striped bars), 10 mg/kg body weight (densely striped bars) and 20 mg/kg body weight (black bars) of C₁₂K(NC₈K)₇NH₂, demonstrating the low toxicity of the polymers of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is of a novel class of polymeric antimicrobial agents, which are designed to exert antimicrobial activity while being stable, non-toxic and avoiding development of resistance thereto, and can therefore be beneficially utilized in the treatment of various medical conditions associated with pathogenic microorganisms. The present invention is further of pharmaceutical compositions, medical devices and food preservatives containing same. The antimicrobial polymers of the present invention preferably include one or more positively charged amino acid residues and one or hydrophobic moiety residues attached one to another.

The principles and operation of the present invention may be better understood with reference to the figures and accompanying descriptions.

Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details set forth in the following description or exemplified by the Examples. The invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.

As discussed above, the use of classical modern antibiotic agents such as tetracycline, gentamycin, ciprofloxacin and methicillin has become during the years severely limited by the development of resistance thereto. Extensive studies have therefore been conducted in a search for novel antimicrobial agents that would circumvent the resistance induction.

As further discussed above, naturally occurring antimicrobial peptides (AMPs) are exceptionally potent antimicrobial agents, but as pharmaceuticals they suffer from the limitations associated with peptide production, maintenance and modes of clinical administration for therapeutic use.

Based on the knowledge which accumulated over the years on the nature of antimicrobial peptides and the limitations associated with their use, the present inventors hypothesized that in order to achieve a novel class of antimicrobial agents devoid of the resistance-inducing drawbacks of classical antibiotic agents, and those of AMPs, three key attributes of AMPs needs to be maintained: a flexible structure, an amphiphatic character and a net positive charge.

While conceiving the present invention, it was envisioned that a flexible polymeric structure will serve the objective of avoiding the development of resistance in the target microorganism. It was further envisioned that use of amino acids, as defined hereinbelow, can serve as a basis for both a polymer as well as a source for net positive charge.

While further conceiving the present invention, it was hypothesized that avoiding a pure amino acid polypeptide structure would not only resolve the production and maintenance issues limiting the use of polypeptides as drugs, but would also alleviate the sever limitations restricting the administration of polypeptides as drugs. Thus, it was envisioned that the desired amphiphatic trait of the envisioned polymer may arise from non-amino acid hydrophobic moieties, such as, but not limited to fatty acids and the likes.

While reducing the present invention to practice, as is demonstrated in the Examples section that follows, the present inventors have developed and successfully produced a novel class of polymers which were shown to exhibit high antimicrobial activity, low resistance induction, non-hemolyticity, resistibility to plasma proteases and high affinity to microbial membranes.

While further conceiving the present invention, it was envisioned that conjugating an active agent to the polymeric structure, such as a labeling agent and/or a therapeutically active agent, will combine the affinity of the polymers of the present invention to microbial cells, and the utility of the additional active agent. In cases where the active agent is a labeling agent, the combination will assist in locating and diagnosing concentration of microbial growth in a host, and in cases where the active agent is a therapeutically active agent, synergistic therapeutic effects could be achieved, resulting from the dual therapeutic effect of the therapeutically active agent and the antimicrobial polymeric structure. In addition, targeted delivery of the therapeutic agent could be achieved.

Thus, according to one aspect of the present invention, there is provided a polymer, having an antimicrobial activity, which comprises a plurality (e.g., two or more) amino acid residues and one or more hydrophobic moiety residues, wherein at least one of the hydrophobic moiety residues is covalently linked to at least two amino acid residues via the N-alpha of one amino acid residue and/or the C-alpha of the other amino acid residue. Therefore, the polymer is a chain made of a sequence of amino acid residues, interrupted by one or more hydrophobic moiety residues.

As used herein throughout the term “amino acid” or “amino acids” is understood to include the 20 genetically coded amino acids; those amino acids often modified post-translationally in vivo, including, for example, hydroxyproline, phosphoserine and phosphothreonine; and other unusual amino acids including, but not limited to, 2-aminoadipic acid, hydroxylysine, isodesmosine, nor-valine, nor-leucine and ornithine. Furthermore, the term “amino acid” includes both D- and L-amino acids and other non-naturally occurring amino acids.

Tables 1 and 2 below list the genetically encoded amino acids (Table 1) and non-limiting examples of non-conventional/modified amino acids (Table 2) which can be used with the present invention.

TABLE 1 Three-Letter One-letter Amino acid Abbreviation Symbol Alanine Ala A Arginine Arg R Asparagine Asn N Aspartic acid Asp D Cysteine Cys C Glutamine Gln Q Glutamic acid Glu E Glycine Gly G Histidine His H Isoleucine Iie I Leucine Leu L Lysine Lys K Methionine Met M Phenylalanine Phe F Proline Pro P Serine Ser S Threonine Thr T Tryptophan Trp W Tyrosine Tyr Y Valine Val V

TABLE 2 Non-conventional amino acid Code Non-conventional amino acid Code α-aminobutyric acid Abu L-N-methylalanine Nmala α-amino-α-methylbutyrate Mgabu L-N-methylarginine Nmarg aminocyclopropane-carboxylate Cpro L-N-methylasparagine Nmasn aminoisobutyric acid Aib L-N-methylaspartic acid Nmasp aminonorbornyl-carboxylate Norb L-N-methylcysteine Nmcys Cyclohexylalanine Chexa L-N-methylglutamine Nmgin Cyclopentylalanine Cpen L-N-methylglutamic acid Nmglu D-alanine Dal L-N-methylhistidine Nmhis D-arginine Darg L-N-methylisolleucine Nmile D-aspartic acid Dasp L-N-methylleucine Nmleu D-cysteine Dcys L-N-methyllysine Nmlys D-glutamine Dgln L-N-methylmethionine Nmmet D-glutamic acid Dglu L-N-methylnorleucine Nmnle D-histidine Dhis L-N-methylnorvaline Nmnva D-isoleucine Dile L-N-methylornithine Nmorn D-leucine Dleu L-N-methylphenylalanine Nmphe D-lysine Dlys L-N-methylproline Nmpro D-methionine Dmet L-N-methylserine Nmser D/L-ornithine D/Lorn L-N-methylthreonine Nmthr D-phenylalanine Dphe L-N-methyltryptophan Nmtrp D-proline Dpro L-N-methyltyrosine Nmtyr D-serine Dser L-N-methylvaline Nmval D-threonine Dthr L-N-methylethylglycine Nmetg D-tryptophan Dtrp L-N-methyl-t-butylglycine Nmtbug D-tyrosine Dtyr L-norleucine Nle D-valine Dval L-norvaline Nva D-α-methylalanine Dmala α-methyl-aminoisobutyrate Maib D-α-methylarginine Dmarg α-methyl-γ-aminobutyrate Mgabu D-α-methylasparagine Dmasn α-methylcyclohexylalanine Mchexa D-α-methylaspartate Dmasp α-methylcyclopentylalanine Mcpen D-α-methylcysteine Dmcys α-methyl-α-napthylalanine Manap D-α-methylglutamine Dmgln α-methylpenicillamine Mpen D-α-methylhistidine Dmhis N-(4-aminobutyl)glycine Nglu D-α-methylisoleucine Dmile N-(2-aminoethyl)glycine Naeg D-α-methylleucine Dmleu N-(3-aminopropyl)glycine Norn D-α-methyllysine Dmlys N-amino-a-methylbutyrate Nmaabu D-α-methylmethionine Dmmet α-napthylalanine Anap D-α-methylornithine Dmorn N-benzylglycine Nphe D-α-methylphenylalanine Dmphe N-(2-carbamylethyl)glycine Ngln D-α-methylproline Dmpro N-(carbamylmethyl)glycine Nasn D-α-methylserine Dmser N-(2-carboxyethyl)glycine Nglu D-α-methylthreonine Dmthr N-(carboxymethyl)glycine Nasp D-α-methyltryptophan Dmtrp N-cyclobutylglycine Ncbut D-α-methyltyrosine Dmty N-cycloheptylglycine Nchep D-α-methylvaline Dmval N-cyclohexylglycine Nchex D-α-methylalnine Dnmala N-cyclodecylglycine Ncdec D-α-methylarginine Dnmarg N-cyclododeclglycine Ncdod D-α-methylasparagine Dnmasn N-cyclooctylglycine Ncoct D-α-methylasparatate Dnmasp N-cyclopropylglycine Ncpro D-α-methylcysteine Dnmcys N-cycloundecylglycine Ncund D-N-methylleucine Dnmleu N-(2,2-diphenylethyl)glycine Nbhm D-N-methyllysine Dnmlys N-(3,3-diphenylpropyl)glycine Nbhe N-methylcyclohexylalanine Nmchexa N-(3-indolylyethyl) glycine Nhtrp D-N-methylornithine Dnmorn N-methyl-γ-aminobutyrate Nmgabu N-methylglycine Nala D-N-methylmethionine Dnmmet N-methylaminoisobutyrate Nmaib N-methylcyclopentylalanine Nmcpen N-(1-methylpropyl)glycine Nile D-N-methylphenylalanine Dnmphe N-(2-methylpropyl)glycine Nile D-N-methylproline Dnmpro N-(2-methylpropyl)glycine Nleu D-N-methylserine Dnmser D-N-methyltryptophan Dnmtrp D-N-methylserine Dnmser D-N-methyltyrosine Dnmtyr D-N-methylthreonine Dnmthr D-N-methylvaline Dnmval N-(1-methylethyl)glycine Nva γ-aminobutyric acid Gabu N-methyla-napthylalanine Nmanap L-t-butylglycine Tbug N-methylpenicillamine Nmpen L-ethylglycine Etg N-(p-hydroxyphenyl)glycine Nhtyr L-homophenylalanine Hphe N-(thiomethyl)glycine Ncys L-α-methylarginine Marg penicillamine Pen L-α-methylaspartate Masp L-α-methylalanine Mala L-α-methylcysteine Mcys L-α-methylasparagine Masn L-α-methylglutamine Mgln L-α-methyl-t-butylglycine Mtbug L-α-methylhistidine Mhis L-methylethylglycine Metg L-α-methylisoleucine Mile L-α-methylglutamate Mglu D-N-methylglutamine Dnmgln L-α-methylhomo phenylalanine Mhphe D-N-methylglutamate Dnmglu N-(2-methylthioethyl)glycine Nmet D-N-methylhistidine Dnmhis N-(3-guanidinopropyl)glycine Narg D-N-methylisoleucine Dnmile N-(1-hydroxyethyl)glycine Nthr D-N-methylleucine Dnmleu N-(hydroxyethyl)glycine Nser D-N-methyllysine Dnmlys N-(imidazolylethyl)glycine Nhis N-methylcyclohexylalanine Nmchexa N-(3-indolylyethyl)glycine Nhtrp D-N-methylornithine Dnmorn N-methyl-γ-aminobutyrate Nmgabu N-methylglycine Nala D-N-methylmethionine Dnmmet N-methylaminoisobutyrate Nmaib N-methylcyclopentylalanine Nmcpen N-(1-methylpropyl)glycine Nile D-N-methylphenylalanine Dnmphe N-(2-methylpropyl)glycine Nleu D-N-methylproline Dnmpro D-N-methyltryptophan Dnmtrp D-N-methylserine Dnmser D-N-methyltyrosine Dnmtyr D-N-methylthreonine Dnmthr D-N-methylvaline Dnmval N-(1-methylethyl)glycine Nval γ-aminobutyric acid Gabu N-methyla-napthylalanine Nmanap L-t-butylglycine Tbug N-methylpenicillamine Nmpen L-ethylglycine Etg N-(p-hydroxyphenyl)glycine Nhtyr L-homophenylalanine Hphe N-(thiomethyl)glycine Ncys L-α-methylarginine Marg penicillamine Pen L-α-methylaspartate Masp L-α-methylalanine Mala L-α-methylcysteine Mcys L-α-methylasparagine Masn L-α-methylglutamine Mgln L-α-methyl-t-butylglycine Mtbug L-α-methylhistidine Mhis L-methylethylglycine Metg L-α-methylisoleucine Mile L-α-methylglutamate Mglu L-α-methylleucine Mleu L-α-methylhomophenylalanine Mhphe L-α-methylmethionine Mmet N-(2-methylthioethyl)glycine Nmet L-α-methylnorvaline Mnva L-α-methyllysine Mlys L-α-methylphenylalanine Mphe L-α-methylnorleucine Mnle L-α-methylserine mser L-α-methylornithine Morn L-α-methylvaline Mtrp L-α-methylproline Mpro L-α-methylleucine Mval Nnbhm L-α-methylthreonine Mthr N-(N-(2,2-diphenylethyl)carbamylmethyl-glycine Nnbhm L-α-methyltyrosine Mtyr 1-carboxy-1-(2,2-diphenyl ethylamino)cyclopropane Nmbc L-N-methylhomophenylalanine Nmhphe N-(N-(3,3-diphenylpropyl)carbamylmethyl(1)glycine Nnbhe D/L-citrulline D/Lctr

As used herein, the phrase “hydrophobic moiety” describes a chemical moiety that has a minor or no affinity to water, that is, which has a low or no dissolvability in water and often in other polar solvents. Exemplary suitable hydrophobic moieties for use in the context of the present invention, include, without limitation, hydrophobic moieties that consist predominantly of one or more hydrocarbon chains and/or aromatic rings, and one or more functional groups which may be non-hydrophobic, but do not alter the overall hydrophobicity of the hydrophobic moiety. Representative examples include, without limitation, fatty acids, hydrophobic amino acids (amino acids with hydrophobic side-chains), alkanes, alkenes, aryls and the likes, as these terms are defined herein, and any combination thereof.

As used herein, the phrase “chemical moiety” describes a residue of a chemical compound, which typically has certain functionality. As is well accepted in the art, the term “residue” refers herein to a major portion of a molecule which is covalently linked to another molecule.

As used herein, the phrase “functional group” describes a chemical group that is capable of undergoing a chemical reaction that typically leads to a bond formation. The bond, according to the present invention, is preferably a covalent bond. Chemical reactions that lead to a bond formation include, for example, nucleophilic and electrophilic substitutions, nucleophilic and electrophilic addition reactions, addition-elimination reactions, cycloaddition reactions, rearrangement reactions and any other known organic reactions that involve a functional group.

A polymer, according to the present invention, may have one or more hydrophobic moiety residues, whereby at least one is linked to one amino acid at one end and to another amino acid residue at another end, and another may elongate the polymeric chain by being linked to either one of the termini, i.e., the N-alpha of a terminal amino acid residue and/or the C-alpha of a terminal amino acid residue. Optionally, a second hydrophobic moiety may be linked to the side-chain of an amino acid residue in the polymer.

The polymer, according to the present invention, preferably includes from 2 to 50 amino acid residues. More preferably, the polymer includes from 2 to 12 amino acid residues, more preferably from 4 to 8 amino acid residues and more preferably from 5 to 7 amino acid residues.

The net positive charge of the polymer is maintained by having one or more positively charged amino acid residues in the polymer, optionally in addition to the positively charged N-terminus amine, when present in its free form.

In one preferred embodiment of the present invention, all the amino acid residues in the polymer are positively charged amino acid residues. An exemplary polymer according to this embodiment includes a plurality of lysine residues.

As used herein the phrase “positively charged amino acid” describes a hydrophilic amino acid with a side chain pKa value of greater than 7, namely a basic amino acid. Basic amino acids typically have positively charged side chains at physiological pH due to association with a hydronium ion. Naturally occurring (genetically encoded) basic amino acids include lysine (Lys, K), arginine (Arg, R) and histidine (His, H), while non-natural (non-genetically encoded, or non-standard) basic amino acids include, for example, ornithine, 2,3,-diaminopropionic acid, 2,4-diaminobutyric acid, 2,5,6-triaminohexanoic acid, 2-amino-4-guanidinobutanoic acid, and homoarginine.

In one embodiment of the present invention, each of the components in the polymer according to the present embodiments is preferably linked to the other by a peptide bond.

The term “peptide bond” as used herein refers to an amide group, namely, a —(C═O)NH— group, which is typically formed by a condensation reaction between a carboxylic group and an amine group, as these terms are defined herein.

However, the polymers of the present embodiments may have other bonds linking the various components in the polymeric structure. Such non-peptidic bonds may render the polymer more stable while in a body or more capable of penetrating into cells. Thus, peptide bonds (—(C═O)NH—) within the polymer may be replaced, for example, by N-methylated amide bonds (—(C═O)NCH₃—), ester bonds (—C(R)H—C(═O)—O—C(R)—N—), ketomethylen bonds (—C(═O)CH₂—), aza bonds (—NH—N(R)—C(═O)—), wherein R is any alkyl, e.g., methyl, carba bonds (—CH₂—NH—), hydroxyethylene bonds (—CH(OH)—CH₂—), thioamide bonds (—CS—NH—), olefinic double bonds (—CH═CH—), retro amide bonds (—NH—(C═O)—), peptide derivatives (—N(R)—CH₂—C(═O)—), wherein R is the “normal” side chain, naturally presented on the carbon atom. These modifications can occur at any of the bonds along the polymer chain and even several (2-3) at the same time.

In a preferred embodiment, all of the bonds in the polymer, linking the amino acid residues and hydrophobic moiety residues to each other, are peptide bonds. For example, in one embodiment, the polymer is made of an amino acid residue linked by a peptide bond to a hydrophobic moiety residue which in turn is linked to a second amino acid residue by another peptide bond. In another example, the polymer of the previous example is elongated by a second hydrophobic moiety residue which is linked to any one of the N- or C-termini by a peptide bond, etcetera.

The polymer, according to the present invention, preferably comprises from 1 to 50 hydrophobic moiety residues. More preferably, the polymer comprises from 1 to 12 hydrophobic moiety residues, more preferably from 4 to 10 hydrophobic moiety residues and more preferably from 6 to 8 hydrophobic moiety residues.

The hydrophobic moieties that are used in the context of this and other aspects of the present invention preferably have one or more hydrocarbon chains, and are capable of linking to one or two other components in the polymer (e.g., one or two of an amino acid residue and another hydrophobic moiety) via two peptide bonds. These moieties therefore preferably have a carboxylic group at one end of the hydrocarbon chain (for linking a free amine group) and an amine group at the other (for linking a carboxylic acid group).

The hydrocarbon chain connecting the carboxylic and amine groups in such a hydrophobic moiety preferably has from 4 to 30 carbon atoms.

In a preferred embodiment of the present invention, the hydrophobic moiety residue is a fatty acid residue wherein the hydrocarbon chain can be unbranched and saturated, branched and saturated, unbranched and unsaturated or branched and unsaturated. More preferably the hydrocarbon chain of the fatty acid residue is an unbranched and saturated chain having from 4 to 30 carbon atoms, preferably from 4 to 20 carbon atoms. Non-limiting example of such fatty acid residues are butyric acid residue, caprylic acid residue and lauric acid residue.

In a more preferred embodiment, the fatty acid residue has an amine on the distal carbon of the hydrocarbon chain (with respect to the carboxylic acid group). Such a fatty acid residue is referred to herein as an ω-amino fatty acid residue. Again here the hydrocarbon chain of the ω-amino fatty acid residue may have from 4 to 30 carbon atoms.

Non-limiting example of such ω-amino fatty acids are 4-amino-butyric acid, 6-amino-caproic acid, 8-amino-caprylic acid, 10-amino-capric acid, 12-amino-lauric acid, 14-amino-myristic acid, 16-amino-palmitic acid, 18-amino-stearic acid, 18-amino-oleic acid, 16-amino-palmitoleic acid, 18-amino-linoleic acid, 18-amino-linolenic acid and 20-amino-arachidonic acid.

According to a preferred embodiment of the present invention, the hydrophobic moiety is selected from the group consisting of 4-amino-butyric acid, 8-amino-caprylic acid and 12-amino-lauric acid and more preferably is 8-amino-caprylic acid and 12-amino-lauric acid.

The polymers described herein can be collectively represented by the following general formula I:

X—W₀-[A₁-Z₁-D₁]-W₁-[A₂-Z₂-D₂]-W₂— . . . [An-Zn-Dn]-Wn-Y  Formula I

wherein:

n is an integer from 2 to 50, preferably from 2 to 12 and more preferably from 2 to 8;

A₁, A₂, . . . , An are each independently an amino acid residue, preferably a positively charged amino acid residue, more preferably all of A₁, A₂, . . . , An are positively charged amino acid residues as discussed hereinabove, such as histidine residues, lysine residues, ornithine residues and arginine residues, and most preferably all the positively charged amino acid residues are lysine residues;

D₁, D₂, . . . Dn are each independently a hydrophobic moiety residue, as defined and discussed hereinabove, or absent, provided that at least one such hydrophobic moiety residue exists in the polymer, preferably at least one of the hydrophobic moiety residues is a ω-amino-fatty acid residue;

Connecting each monomer of the residue are linking moieties, denoted Z₁, Z₂, . . . Zn and W₀, W₁, W₂, . . . Wn, each of which independently linking an amino acid residue and a hydrophobic moiety residue or absent, preferably at least one of the linking moieties is a peptide bond and most preferable all the linking moieties are peptide bonds;

The fringes of the polymer, denoted X and Y, may each independently be hydrogen, an amine, an amino acid residue, a hydrophobic moiety residue, is another polymer having the general Formula I or absent.

As discussed above, one or more of the hydrophobic moiety residues may be attached to a side chain of one or more of the amino acid residues of the polymer, i.e., act as a branch of the main polymer.

The presently most preferred polymers are polymers in which n is an integer from 5 to 7, the amino acid residues are all lysine residues, the hydrophobic moiety residues are all 8-amino-caprylic acid residues, X is a hydrophobic moiety such as, for example, a fatty acid residue (a dodecanoic acid residue), and/or Y is amine or absent.

Particularly preferred polymers according to the present embodiments are those having the Formulae hereinbelow:

which is also referred to herein as C₁₂K(NC₈K)₇NH₂; and

which is also referred to herein as C₁₂K(NC₈K)₅NH₂.

The polymers according to the present embodiments can be readily synthesized. For example, polymers in which the linking moieties are peptide bonds, and hence resemble natural and synthetic peptides in this respect, can be prepared by classical methods known in the art for peptide syntheses. Such methods include, for example, standard solid phase techniques. The standard methods include exclusive solid phase synthesis, partial solid phase synthesis methods, fragment condensation, classical solution synthesis, and even by recombinant DNA technology. See, e.g., Merrifield, J. Am. Chem. Soc., 85:2149 (1963), incorporated herein by reference. Solid phase peptide synthesis procedures are well known in the art and further described by John Morrow Stewart and Janis Dillaha Young, Solid Phase Peptide Syntheses (2nd Ed., Pierce Chemical Company, 1984).

The polymers of the present invention can be purified, for example, by preparative high performance liquid chromatography [Creighton T. (1983) Proteins, structures and molecular principles. WH Freeman and Co. N.Y.].

Apart from having beneficial antimicrobial activity per se, as detailed herein, the polymers of the present invention may include an additional active agent such as a labeling agent and/or a therapeutically active agent attached thereto. The conjugation of the active agent to a polymer of the present invention can provide a dual utility for the polymer. When the additional active agent is a labeling agent, the conjugation thereof to an antimicrobial polymer of the present invention, having a high affinity to microbial cells, can assist in the location, diagnosis and targeting of microbial growth loci in a host. When the additional active agent is a therapeutically active agent, the conjugation thereof to an antimicrobial polymer of the present invention will exert a dual and possibly synergistic antimicrobial activity.

According to preferred embodiments of the present invention, the one or more active agents may be attached to the polymer at any substitutable position. Examples of such substitutable positions include, without limitation, a side chain of any one or more of the amino acid residues in the polymer, any one of the linking moieties of the polymer, any one of the N- and C-termini of the polymer and any one or more of the hydrophobic moiety residues in the polymer.

Hence, as used herein, the phrase “a therapeutically active agent” describes a chemical substance, which exhibit a therapeutic activity when administered to a subject

As used herein, the phrase “labeling agent” refers to a detectable moiety or a probe and includes, for example, chromophores, fluorescent compounds, phosphorescent compounds, heavy metal clusters, and radioactive labeling compounds, as well as any other known detectable moieties.

Labeling of microbial growth loci in a host is critical for the diagnosis and efficient targeting of the photogenic microorganism and treatment thereof.

Adding a therapeutically active agent to the polymer can provide a solution for many deficiencies of presently known therapeutically active agent against photogenic microorganisms, such as resistance of the photogenic microorganism to the therapeutically active agent, specificity of the therapeutically active agent to photogenic microorganism and general efficacy weakness. The polymers of the present invention can exhibit not only antimicrobial activity per se by virtue of their structure and chemical properties, but can also provide targeting capacity as a delivery vehicle to a presently know therapeutically active agents and further provide membrane permeability to presently know therapeutically active agents due to their capability to exert disturbance in the membrane structure of photogenic microorganisms.

Non-limiting examples of therapeutically active agents that can be beneficially used in this and other contexts of the present invention include, without limitation, one or more of an agonist residue, an amino acid residue, an analgesic residue, an antagonist residue, an antibiotic agent residue, an antibody residue, an antidepressant agent, an antigen residue, an anti-histamine residue, an anti-hypertensive agent, an anti-inflammatory drug residue, an anti-metabolic agent residue, an antimicrobial agent residue, an antioxidant residue, an anti-proliferative drug residue, an antisense residue, a chemotherapeutic drug residue, a co-factor residue, a cytokine residue, a drug residue, an enzyme residue, a growth factor residue, a heparin residue, a hormone residue, an immunoglobulin residue, an inhibitor residue, a ligand residue, a nucleic acid residue, an oligonucleotide residue, a peptide residue, a phospholipid residue, a prostaglandin residue, a protein residue, a toxin residue, a vitamin residue and any combination thereof.

The combined therapeutic effect is particularly advantageous when the therapeutically active agent is an antimicrobial or an antibiotic agent. The combined activity of the polymers of the present invention and that of an additional antimicrobial/antibiotic agent may provide the antimicrobial/antibiotic agent the capacity to overcome the known limitations of these drugs such as targeting, specificity, efficacy, drug-resistance etcetera. Synergism may also be achieved.

Non-limiting examples of antimicrobial and antibiotic agents that are suitable for use in this context of the present invention include, without limitation, mandelic acid, 2,4-dichlorobenzenemethanol, 4-[bis(ethylthio)methyl]-2-methoxyphenol, 4-epi-tetracycline, 4-hexylresorcinol, 5,12-dihydro-5,7,12,14-tetrazapentacen, 5-chlorocarvacrol, 8-hydroxyquinoline, acetarsol, acetylkitasamycin, acriflavin, alatrofloxacin, ambazon, amfomycin, amikacin, amikacin sulfate, aminoacridine, aminosalicylate calcium, aminosalicylate sodium, aminosalicylic acid, ammoniumsulfobituminat, amorolfin, amoxicillin, amoxicillin sodium, amoxicillin trihydrate, amoxicillin-potassium clavulanate combination, amphotericin B, ampicillin, ampicillin sodium, ampicillin trihydrate, ampicillin-sulbactam, apalcillin, arbekacin, aspoxicillin, astromicin, astromicin sulfate, azanidazole, azidamfenicol, azidocillin, azithromycin, azlocillin, aztreonam, bacampicillin, bacitracin, bacitracin zinc, bekanamycin, benzalkonium, benzethonium chloride, benzoxonium chloride, berberine hydrochloride, biapenem, bibrocathol, biclotymol, bifonazole, bismuth subsalicylate, bleomycin antibiotic complex, bleomycin hydrochloride, bleomycin sulfate, brodimoprim, bromochlorosalicylanilide, bronopol, broxyquinolin, butenafine, butenafine hydrochloride, butoconazol, calcium undecylenate, candicidin antibiotic complex, capreomycin, carbenicillin, carbenicillin disodium, carfecillin, carindacillin, carumonam, carzinophilin, caspofungin acetate, cefacetril, cefaclor, cefadroxil, cefalexin, cefalexin hydrochloride, cefalexin sodium, cefaloglycin, cefaloridine, cefalotin, cefalotin sodium, cefamandole, cefamandole nafate, cefamandole sodium, cefapirin, cefapirin sodium, cefatrizine, cefatrizine propylene glycol, cefazedone, cefazedone sodium salt, cefazolin, cefazolin sodium, cefbuperazone, cefbuperazone sodium, cefcapene, cefcapene pivoxil hydrochloride, cefdinir, cefditoren, cefditoren pivoxil, cefepime, cefepime hydrochloride, cefetamet, cefetamet pivoxil, cefixime, cefmenoxime, cefmetazole, cefmetazole sodium, cefminox, cefminox sodium, cefmolexin, cefodizime, cefodizime sodium, cefonicid, cefonicid sodium, cefoperazone, cefoperazone sodium, ceforanide, cefoselis sulfate, cefotaxime, cefotaxime sodium, cefotetan, cefotetan disodium, cefotiam, cefotiam hexetil hydrochloride, cefotiam hydrochloride, cefoxitin, cefoxitin sodium, cefozopran hydrochloride, cefpiramide, cefpiramide sodium, cefpirome, cefpirome sulfate, cefpodoxime, cefpodoxime proxetil, cefprozil, cefquinome, cefradine, cefroxadine, cefsulodin, ceftazidime, cefteram, cefteram pivoxil, ceftezole, ceftibuten, ceftizoxime, ceftizoxime sodium, ceftriaxone, ceftriaxone sodium, cefuroxime, cefuroxime axetil, cefuroxime sodium, cetalkonium chloride, cetrimide, cetrimonium, cetylpyridinium, chloramine T, chloramphenicol, chloramphenicol palmitate, chloramphenicol succinate sodium, chlorhexidine, chlormidazole, chlormidazole hydrochloride, chloroxylenol, chlorphenesin, chlorquinaldol, chlortetracycline, chlortetracycline hydrochloride, ciclacillin, ciclopirox, cinoxacin, ciprofloxacin, ciprofloxacin hydrochloride, citric acid, clarithromycin, clavulanate potassium, clavulanate sodium, clavulanic acid, clindamycin, clindamycin hydrochloride, clindamycin palmitate hydrochloride, clindamycin phosphate, clioquinol, cloconazole, cloconazole monohydrochloride, clofazimine, clofoctol, clometocillin, clomocycline, clotrimazol, cloxacillin, cloxacillin sodium, colistin, colistin sodium methanesulfonate, colistin sulfate, cycloserine, dactinomycin, danofloxacin, dapsone, daptomycin, daunorubicin, DDT, demeclocycline, demeclocycline hydrochloride, dequalinium, dibekacin, dibekacin sulfate, dibrompropamidine, dichlorophene, dicloxacillin, dicloxacillin sodium, didecyldimethylammonium chloride, dihydrostreptomycin, dihydrostreptomycin sulfate, diiodohydroxyquinolin, dimetridazole, dipyrithione, dirithromycin, DL-menthol, D-menthol, dodecyltriphenylphosphonium bromide, doxorubicin, doxorubicin hydrochloride, doxycycline, doxycycline hydrochloride, econazole, econazole nitrate, enilconazole, enoxacin, enrofloxacin, eosine, epicillin, ertapenem sodium, erythromycin, erythromycin estolate, erythromycin ethyl succinate, erythromycin lactobionate, erythromycin stearate, ethacridine, ethacridine lactate, ethambutol, ethanoic acid, ethionamide, ethyl alcohol, eugenol, exalamide, faropenem, fenticonazole, fenticonazole nitrate, fezatione, fleroxacin, flomoxef, flomoxef sodium, florfenicol, flucloxacillin, flucloxacillin magnesium, flucloxacillin sodium, fluconazole, flucytosine, flumequine, flurithromycin, flutrimazole, fosfomycin, fosfomycin calcium, fosfomycin sodium, framycetin, framycetin sulphate, furagin, furazolidone, fusafungin, fusidic acid, fusidic acid sodium salt, gatifloxacin, gemifloxacin, gentamicin antibiotic complex, gentamicin c 1a, gentamycin sulfate, glutaraldehyde, gramicidin, grepafloxacin, griseofulvin, halazon, haloprogine, hetacillin, hetacillin potassium, hexachlorophene, hexamidine, hexetidine, hydrargaphene, hydroquinone, hygromycin, imipenem, isepamicin, isepamicin sulfate, isoconazole, isoconazole nitrate, isoniazid, isopropanol, itraconazole, josamycin, josamycin propionate, kanamycin, kanamycin sulphate, ketoconazole, kitasamycin, lactic acid, lanoconazole, lenampicillin, leucomycin A1, leucomycin A13, leucomycin A4, leucomycin A5, leucomycin A6, leucomycin A7, leucomycin A8, leucomycin A9, levofloxacin, lincomycin, lincomycin hydrochloride, linezolid, liranaftate, l-menthol, lomefloxacin, lomefloxacin hydrochloride, loracarbef, lymecyclin, lysozyme, mafenide acetate, magnesium monoperoxophthalate hexahydrate, mecetronium ethylsulfate, mecillinam, meclocycline, meclocycline sulfosalicylate, mepartricin, merbromin, meropenem, metalkonium chloride, metampicillin, methacycline, methenamin, methyl salicylate, methylbenzethonium chloride, methylrosanilinium chloride, meticillin, meticillin sodium, metronidazole, metronidazole benzoate, mezlocillin, mezlocillin sodium, miconazole, miconazole nitrate, micronomicin, micronomicin sulfate, midecamycin, minocycline, minocycline hydrochloride, miocamycin, miristalkonium chloride, mitomycin c, monensin, monensin sodium, morinamide, moxalactam, moxalactam disodium, moxifloxacin, mupirocin, mupirocin calcium, nadifloxacin, nafcillin, nafcillin sodium, naftifine, nalidixic acid, natamycin, neomycin a, neomycin antibiotic complex, neomycin C, neomycin sulfate, neticonazole, netilmicin, netilmicin sulfate, nifuratel, nifuroxazide, nifurtoinol, nifurzide, nimorazole, niridazole, nitrofurantoin, nitrofurazone, nitroxolin, norfloxacin, novobiocin, nystatin antibiotic complex, octenidine, ofloxacin, oleandomycin, omoconazol, orbifloxacin, ornidazole, ortho-phenylphenol, oxacillin, oxacillin sodium, oxiconazole, oxiconazole nitrate, oxoferin, oxolinic acid, oxychlorosene, oxytetracycline, oxytetracycline calcium, oxytetracycline hydrochloride, panipenem, paromomycin, paromomycin sulfate, pazufloxacine, pefloxacin, pefloxacin mesylate, penamecillin, penicillin G, penicillin G potassium, penicillin G sodium, penicillin V, penicillin V calcium, penicillin V potassium, pentamidine, pentamidine diisetionate, pentamidine mesilas, pentamycin, phenethicillin, phenol, phenoxyethanol, phenylmercuriborat, PHMB, phthalylsulfathiazole, picloxydin, pipemidic acid, piperacillin, piperacillin sodium, pipercillin sodium-tazobactam sodium, piromidic acid, pivampicillin, pivcefalexin, pivmecillinam, pivmecillinam hydrochloride, policresulen, polymyxin antibiotic complex, polymyxin B, polymyxin B sulfate, polymyxin B1, polynoxylin, povidone-iodine, propamidin, propenidazole, propicillin, propicillin potassium, propionic acid, prothionamide, protiofate, pyrazinamide, pyrimethamine, pyrithion, pyrroInitrin, quinoline, quinupristin-dalfopristin, resorcinol, ribostamycin, ribostamycin sulfate, rifabutin, rifampicin, rifamycin, rifapentine, rifaximin, ritiometan, rokitamycin, rolitetracycline, rosoxacin, roxithromycin, rufloxacin, salicylic acid, secnidazol, selenium disulphide, sertaconazole, sertaconazole nitrate, siccanin, sisomicin, sisomicin sulfate, sodium thiosulfate, sparfloxacin, spectinomycin, spectinomycin hydrochloride, spiramycin antibiotic complex, spiramycin b, streptomycin, streptomycin sulphate, succinylsulfathiazole, sulbactam, sulbactam sodium, sulbenicillin disodium, sulbentin, sulconazole, sulconazole nitrate, sulfabenzamide, sulfacarbamide, sulfacetamide, sulfacetamide sodium, sulfachlorpyridazine, sulfadiazine, sulfadiazine silver, sulfadiazine sodium, sulfadicramide, sulfadimethoxine, sulfadoxine, sulfaguanidine, sulfalene, sulfamazone, sulfamerazine, sulfamethazine, sulfamethazine sodium, sulfamethizole, sulfamethoxazole, sulfamethoxazol-trimethoprim, sulfamethoxypyridazine, sulfamonomethoxine, sulfamoxol, sulfanilamide, sulfaperine, sulfaphenazol, sulfapyridine, sulfaquinoxaline, sulfasuccinamide, sulfathiazole, sulfathiourea, sulfatolamide, sulfatriazin, sulfisomidine, sulfisoxazole, sulfisoxazole acetyl, sulfonamides, sultamicillin, sultamicillin tosilate, tacrolimus, talampicillin hydrochloride, teicoplanin A2 complex, teicoplanin A2-1, teicoplanin A2-2, teicoplanin A2-3, teicoplanin A2-4, teicoplanin A2-5, teicoplanin A3, teicoplanin antibiotic complex, telithromycin, temafloxacin, temocillin, tenoic acid, terbinafine, terconazole, terizidone, tetracycline, tetracycline hydrochloride, tetracycline metaphosphate, tetramethylthiuram monosulfide, tetroxoprim, thiabendazole, thiamphenicol, thiaphenicol glycinate hydrochloride, thiomersal, thiram, thymol, tibezonium iodide, ticarcillin, ticarcillin-clavulanic acid mixture, ticarcillin disodium, ticarcillin monosodium, tilbroquinol, tilmicosin, tinidazole, tioconazole, tobramycin, tobramycin sulfate, tolciclate, tolindate, tolnaftate, toloconium metilsulfat, toltrazuril, tosufloxacin, triclocarban, triclosan, trimethoprim, trimethoprim sulfate, triphenylstibinsulfide, troleandomycin, trovafloxacin, tylosin, tyrothricin, undecoylium chloride, undecylenic acid, vancomycin, vancomycin hydrochloride, viomycin, virginiamycin antibiotic complex, voriconazol, xantocillin, xibornol and zinc undecylenate.

Major parts of the polymers of the present embodiments are based on a repetitive element consisting of a conjugate between an amino acid and a bi-functional hydrophobic moiety. The conjugate may repeat several times in the sequence of the polymer and/or be interrupted and/or flanked by a difference types of conjugates or by single or repeats of amino acid residues and single or repeats of hydrophobic moiety residues.

Hence, according to another aspect of the present invention, there is provided a conjugate which includes an amino acid residue and a hydrophobic moiety residue, as defined and described hereinabove, attached to the N-alpha or the C-alpha of the amino acid residue. The hydrophobic moiety residue in the conjugate of the present invention is designed such that is it capable of forming a bond with an N-alpha or a C-alpha of an additional amino acid residue. Preferably, the hydrophobic moiety residue is conjugated to the amino acid residue via a peptide bond.

The hydrophobic moiety of the conjugate of the present invention is having a bi-functional design which allows the conjugate to serve as a polymerizable conjugate that can form a part of the polymers described and presented herein. Preferably, the hydrophobic moiety which forms a part of the conjugate is having a bi-functionality in the form of a carboxylic group at one end thereof and an amine group at the other end thereof.

Hence, according to another aspect of the present invention, there is provided a process of preparing the conjugate described hereinabove, the general process is based on providing an amino acid, preferably the amino acid is a positively charged amino acid, such as histidine, lysine, ornithine and arginine; providing a hydrophobic moiety as defined and discussed hereinabove having a first functional group that is capable of reacting with an N-alpha of an amino acid residue and a second functional group capable of reacting with a C-alpha of an amino acid; linking the first functional group in the hydrophobic moiety to the amino acid via the N-alpha of the amino acid; or linking the second functional group in the hydrophobic moiety to the amino acid via the C-alpha of the amino acid.

Preferably, the link between the N-alpha or the C-alpha of the amino acid and the hydrophobic moiety is via a peptide bond.

In order to form a peptide bond linking the amino acid to the hydrophobic moiety, the hydrophobic moiety preferably has a carboxylic group at one end thereof and an amine group at the other end thereof.

The antimicrobial polymers as described herein can be beneficially utilized in the treatment of pathogenic microorganism infections, as these are defined hereinbelow. As demonstrated in the Example section that follows, such polymers are by themselves capable of exerting antimicrobial activity. The option to include an additional therapeutically active agent may thus act synergistically as toxic agents against various bacteria, fungi and other microorganisms.

Herein throughout, the phrase “pathogenic microorganism” is used to describe any microorganism which can cause a disease or disorder in a higher organism, such as mammals in general and a human in particular. The pathogenic microorganism may belong to any family of organisms such as, but not limited to prokaryotic organisms, eubacterium, archaebacterium, eukaryotic organisms, yeast, fungi, algae, protozoan, and other parasites. Non-limiting examples of pathogenic microorganism are Plasmodium falciparum and related malaria-causing protozoan parasites, Acanthamoeba and other free-living amoebae, Aeromonas hydrophila, Anisakis and related worms, Acinetobacter baumanii, Ascaris lumbricoides, Bacillus cereus, Brevundimonas diminuta, Campylobacter jejuni, Clostridium botulinum, Clostridium perfringens, Cryptosporidium parvum, Cyclospora cayetanensis, Diphyllobothrium, Entamoeba histolytica, certain strains of Escherichia coli, Eustrongylides, Giardia lamblia, Klebsiella pneumoniae, Listeria monocytogenes, Nanophyetus, Plesiomonas shigelloides, Proteus mirabilis, Pseudomonas aeruginosa, Salmonella, Serratia odorifera, Shigella, Staphylococcus aureus, Stenotrophomonas maltophilia, Streptococcus, Trichuris trichiura, Vibrio cholerae, Vibrio parahaemolyticus, Vibrio vulnificus and other vibrios, Yersinia enterocolitica, Yersinia pseudotuberculosis and Yersinia kristensenii.

Hence, according to another aspect of the present invention, there is provided a method of treating a medical condition associated with a pathogenic microorganism, the method includes administering to a subject in need thereof a therapeutically effective amount of one or more of the polymers, as described hereinabove

As used herein, the terms “treating” and “treatment” includes abrogating, substantially inhibiting, slowing or reversing the progression of a condition, substantially ameliorating clinical or aesthetical symptoms of a condition or substantially preventing the appearance of clinical or aesthetical symptoms of a condition.

As used herein, the phrase “therapeutically effective amount” describes an amount of the composite being administered which will relieve to some extent one or more of the symptoms of the condition being treated.

The method of treatment, according to an embodiment of the present invention, may include the administration of an additional therapeutically active agent, as this is defined and discussed hereinabove.

As mentioned above and demonstrated in the Example section that follows, the antimicrobial polymers of the present invention, alone or in combination with any other therapeutically active agents, can be designed and utilized to destroy pathological microorganisms. The destruction of a pathogenic microorganism is effected by selectively destructing a portion of the cells of a pathogenic microorganism. While most known antibiotics act by interfering selectively with the biosynthesis of one or more of the molecular constituents of the cell-membrane, proteins or nucleic acids, the polymers of the present invention also act by binding and disrupting the outer membrane of the pathogenic microorganism cells. Disrupting the outer membrane of a cell causes its death due to membrane depolarization, leakage of metabolites and/or total loss of cell integrity; therefore the polymers of the present invention also act directly as effective antimicrobial agents by disrupting the metabolism and/or the multiplication processes of the pathogenic microorganism.

As mentioned above and demonstrated in the Example section that follows, the polymers presented herein may act as antimicrobial agents which do not evoke the appearance of resistance thereto. The possible development of resistance to the polymers of the present invention was tested by measuring the minimal inhibitory concentration (MIC) levels following multiple exposures of the bacteria to exemplary polymers according to the present invention. The results obtained in the antimicrobial-resistance studies in bacteria presented hereinbelow, showed that exposing bacteria, and even strains that already developed resistance to classical antibiotics, to the antimicrobial polymers presented herein did not result in development of resistance.

As is further mentioned above and demonstrated in the Example section that follows, the polymers presented herein are non-toxic to mammals.

As is further demonstrated in the Examples section that follows, the polymers of the present invention can act synergistically with another antibiotic or other therapeutically active agent by permeabilizing the cells of the pathogenic microorganism; hence exhibit additionally an indirect antimicrobial activity. The results presented hereinbelow permit the conclusion that the polymers of the present invention are potent outer-membrane disintegrating agents. The permeabilizing action of the polymers can increase the uptake of other therapeutically active agents and therefore should be able to potentiate the apparent antimicrobial activity of other drugs and antibiotics.

Medical conditions associated with a pathogenic microorganism include infections, infestation, contaminations and transmissions by or of pathogenic microorganism. In general, a disease causing infection is the invasion into the tissues of a plant or an animal by pathogenic microorganisms. The invasion of body tissues by parasitic worms and other higher pathogenic organisms is commonly referred to as infestation.

Invading organisms such as bacteria produce toxins that damage host tissues and interfere with normal metabolism; some toxins are actually enzymes that break down host tissues. Other bacterial substances may inflict their damage by destroying the host's phagocytes, rendering the body more susceptible to infections by other pathogenic microorganisms. Substances produced by many invading organisms cause allergic sensitivity in the host. Infections may be spread via respiratory droplets, direct contact, contaminated food, or vectors, such as insects. They can also be transmitted sexually and from mother to fetus.

Diseases caused by bacterial infections typically include, for example, actinomycosis, anthrax, aspergillosis, bacteremia, bacterial skin diseases, bartonella infections, botulism, brucellosis, burkholderia infections, campylobacter infections, candidiasis, cat-scratch disease, chlamydia infections, cholera, clostridium infections, coccidioidomycosis, cryptococcosis, dermatomycoses, diphtheria, ehrlichiosis, epidemic louse borne typhus, Escherichia coli infections, fusobacterium infections, gangrene, general infections, general mycoses, gonorrhea, gram-negative bacterial infections, gram-positive bacterial infections, histoplasmosis, impetigo, klebsiella infections, legionellosis, leprosy, leptospirosis, listeria infections, lyme disease, malaria, maduromycosis, melioidosis, mycobacterium infections, mycoplasma infections, necrotizing fasciitis, nocardia infections, onychomycosis, ornithosis, pneumococcal infections, pneumonia, pseudomonas infections, Q fever, rat-bite fever, relapsing fever, rheumatic fever, rickettsia infections, Rocky-mountain spotted fever, salmonella infections, scarlet fever, scrub typhus, sepsis, sexually transmitted bacterial diseases, staphylococcal infections, streptococcal infections, surgical site infection, tetanus, tick-borne diseases, tuberculosis, tularemia, typhoid fever, urinary tract infection, vibrio infections, yaws, Yersinia infections, Yersinia pestis plague, zoonoses and zygomycosis.

The polymers of the present embodiments can therefore be used to treat medical conditions caused by pathogenic microorganisms by virtue of their anti-microbial effects inflicted upon the pathogenic microorganisms by one of the abovementioned mechanism which mostly stem from their specific and selective affinity to the membrane of the pathogenic microorganism, and relative undamaging effect they have on mammalian cell, as demonstrated for red blood cells and presented in the Examples section that follows. This affinity can be used to weaken, disrupt, puncture, melt, fuse and/or mark the membrane of a pathogenic microorganism.

The pathogenic microorganism may be destroyed directly by the disruption of its membrane as demonstrated and presented for a series of bacterial strains in the Examples section that follows, or be weakened so as to allow the innate immune system to destroy it or slow down its metabolism and therefore its reproduction so as to allow the innate immune system to overcome the infection.

The pathogenic microorganism may be destroyed by the disruption of its membrane so as to allow a therapeutically active agent, such as an antibiotic agent, to more easily penetrate the cell of the microorganism and afflict its activity thereon.

The latter capacity of the antimicrobial polymer of the present invention to assist the penetration of another therapeutically active agent into the cells of the pathogenic microorganism can be utilized to treat many infectious diseases, such as, for example, malaria.

The experimental results presented in the Examples section that follows suggests that secondary structure might not be an absolute prerequisite for antimicrobial properties. On another hand, evident from these results stems that the only property which is shared by all typical AMPs, and also shared by the polymers of the present invention, is the relative abundance of both hydrophobic and positively charged amino acid residues. Thus, according to the present invention, the antimicrobial polymers presented are endowed with varied positive charge and hydrophobicity and substantially lack secondary structure.

Malaria, also called jungle fever, paludism and swamp fever, is an infectious disease characterized by cycles of chills, fever, and sweating, caused by the parasitic infection of red blood cells by the protozoan parasite, Plasmodium (one of the Apicomplexa), which is transmitted by the bite of an infected vector for human malarial parasite, a female Anopheles mosquito. Of the four types of malaria, the most life-threatening type is falciparum malaria. The other three types of malaria, vivax, malariae, and ovale, are generally less serious and are not life-threatening. Malaria, the deadliest infectious disease yet to be beaten, causes about half a billion infections and between one and two millions deaths annually, mainly in the tropics and sub-Saharan Africa. The Plasmodium falciparum variety of the parasite accounts for 80% of cases and 90% of deaths. The stickiness of the red blood cells is particularly pronounced in P. falciparum malaria and this is the main factor giving rise to hemorrhagic complications of malaria.

To date there is no absolute cure for malaria. If diagnosed early, malaria can be alleviated, but prevention still more effective than treatment, thus substances that inhibit the parasite are widely used by visitors to the tropics. Since the 17^(th) century quinine has been the prophylactic of choice for malaria. The development of quinacrine, chloroquine, and primaquine in the 20^(th) century reduced the reliance on quinine. These anti-malarial medications can be taken preventively, which is recommended for travelers to affected regions.

Unfortunately as early as the 1960s several strains of the malarial parasite developed resistance to chloroquine. This development of resistance, plus the growing immunity of mosquitoes to insecticides, has caused malaria to become one the of world's leading re-emerging infectious diseases. Mefloquine may be used in areas where the disease has become highly resistant to chloroquine, but some strains are now resistant to it and other drugs. Artemisinin (derived from sweet wormwood) in combination with other drugs is now in many cases the preferred treat for resistant strains. Malarone (atovaquone and proguanil) is also used for resistant strains. Vaccines against malaria are still experimental.

While reducing the present invention to practice, the present inventors have prepared and successfully used these anti-microbial polymers as anti-malarial agents with reduced hemolysis effect as demonstrated in the Examples section that follows. It is shown that the polymers of the present invention were able to kill the parasite in a manner that is clearly dissociated from lysis of the host cell. These polymers were able to enter the infected cell but to selectively permeabilize the parasite cell membrane. These results are best explained by the differential interaction of the peptides-like polymer with the distinct properties of the structure and composition of the membranes of intra-erythrocytic malaria parasite Plasmodium falciparum as compared to those of the host and normal red blood cells. These findings also established that the membrane active polymers of the present invention could be engineered to act specifically on the membrane of the intracellular parasite to perturb its functions. The polymers of the present invention can therefore overcome the problem of parasitic resistance to various anti-malarial agents by, for example, weakening the parasite's membrane and enabling the anti-malarial agents to penetrate the parasite's membrane more rapidly.

Therefore, a preferred embodiment of the present invention is the use of the antimicrobial polymers as an anti-malarial agent, either per-se or in combination with a presently used anti-malarial agent or any other anti-parasitic agent, as exemplified in the Examples section that follows.

In any of the aspects of the present invention, the antimicrobial polymers of the present invention can be utilized either per se, or as an active ingredient that forms a part of a pharmaceutical composition, with or without an additional therapeutically active agent, and a pharmaceutically acceptable carrier.

Hence, according to still another aspect of the present invention, there are provided pharmaceutical compositions, which comprise one or more of the polymers of the present invention as described above having an antimicrobial activity and a pharmaceutically acceptable carrier.

As used herein a “pharmaceutical composition” refers to a preparation of the antimicrobial polymer described herein, with other chemical components such as pharmaceutically acceptable and suitable carriers and excipients. The purpose of a pharmaceutical composition is to facilitate administration of a compound to an organism.

Hereinafter, the term “pharmaceutically acceptable carrier” refers to a carrier or a diluent that does not cause significant irritation to an organism and does not abrogate the biological activity and properties of the administered compound. Examples, without limitations, of carriers are: propylene glycol, saline, emulsions and mixtures of organic solvents with water, as well as solid (e.g., powdered) and gaseous carriers.

Herein the term “excipient” refers to an inert substance added to a pharmaceutical composition to further facilitate administration of a compound. Examples, without limitation, of excipients include calcium carbonate, calcium phosphate, various sugars and types of starch, cellulose derivatives, gelatin, vegetable oils and polyethylene glycols.

Techniques for formulation and administration of drugs may be found in “Remington's Pharmaceutical Sciences” Mack Publishing Co., Easton, Pa., latest edition, which is incorporated herein by reference.

Pharmaceutical compositions for use in accordance with the present invention thus may be formulated in conventional manner using one or more pharmaceutically acceptable carriers comprising excipients and auxiliaries, which facilitate processing of the silver-coated enzymes into preparations which, can be used pharmaceutically. Proper formulation is dependent upon the route of administration chosen. Toxicity and therapeutic efficacy of the silver-coated enzymes described herein can be determined by standard pharmaceutical procedures in experimental animals, e.g., by determining the EC₅₀, the IC₅₀ and the LD₅₀ (lethal dose causing death in 50% of the tested animals) for a subject silver-coated enzyme. The data obtained from these activity assays and animal studies can be used in formulating a range of dosage for use in human.

The dosage may vary depending upon the dosage form employed and the route of administration utilized. The exact formulation, route of administration and dosage can be chosen by the individual physician in view of the patient's condition. (See e.g., Fingl et al., 1975, in “The Pharmacological Basis of Therapeutics”, Ch. 1 p. 1).

The amount of a composition to be administered will, of course, be dependent on the subject being treated, the severity of the affliction, the manner of administration, the judgment of the prescribing physician, etc.

Compositions of the present invention may, if desired, be presented in a pack or dispenser device, such as an FDA (the U.S. Food and Drug Administration) approved kit, which may contain one or more unit dosage forms containing the active ingredient. The pack may, for example, comprise metal or plastic foil, such as, but not limited to a blister pack or a pressurized container (for inhalation). The pack or dispenser device may be accompanied by instructions for administration. The pack or dispenser may also be accompanied by a notice associated with the container in a form prescribed by a governmental agency regulating the manufacture, use or sale of pharmaceuticals, which notice is reflective of approval by the agency of the form of the compositions for human or veterinary administration. Such notice, for example, may be of labeling approved by the U.S. Food and Drug Administration for prescription drugs or of an approved product insert. Compositions comprising a silver-coated enzyme of the invention formulated in a compatible pharmaceutical carrier may also be prepared, placed in an appropriate container, and labeled for treatment of an indicated condition or diagnosis, as is detailed hereinabove.

Thus, according to an embodiment of the present invention, depending on the selected polymers and the presence of additional active ingredients, the pharmaceutical compositions of the present invention are packaged in a packaging material and identified in print, in or on the packaging material, for use in the treatment of a medical condition associated with a pathogenic microorganism, as is defined hereinabove and a parasite.

The pharmaceutical composition comprising a polymer of the present invention may further comprise at least one additional therapeutically active agent, as this is defined and presented hereinabove.

The polymers of the present invention can be further beneficially utilized as active substances in various medical devices.

Hence, according to an additional aspect of the present invention there is provided a medical device which includes one or more of the polymers of the present invention, described hereinabove, and a delivery system configured for delivering the polymer(s) to a bodily site of a subject.

The medical devices according to the present invention are therefore used for delivering to or applying on a desired bodily site the polymers of the present invention. The polymers can be incorporated in the medical devices either per se or as a part of a pharmaceutical composition, as described hereinabove.

As used herein, the phrase “bodily site” includes any organ, tissue, membrane, cavity, blood vessel, tract, biological surface or muscle, which delivering thereto or applying thereon the polymers of the present invention is beneficial.

Exemplary bodily sites include, but are not limited to, the skin, a dermal layer, the scalp, an eye, an ear, a mouth, a throat, a stomach, a small intestines tissue, a large intestines tissue, a kidney, a pancreas, a liver, the digestive system, the respiratory tract, a bone marrow tissue, a mucosal membrane, a nasal membrane, the blood system, a blood vessel, a muscle, a pulmonary cavity, an artery, a vein, a capillary, a heart, a heart cavity, a male or female reproductive organ and any visceral organ or cavity.

The medical devices according to this aspect of the present invention can be any medical device known in the art, including those defined and classified, for example, by the FDA and specified in http://www.fda.gov/cdrh/devadvice/313.html (e.g., Class I, II and III), depending e.g., on the condition and bodily site being treated.

Thus, for example, in one embodiment of this aspect of the present invention, the medical device comprises a delivery system that is configured to deliver the polymer(s) by inhalation. Such inhalation devices are useful for delivering the polymers of the present invention to, e.g., the respiratory tract.

The delivery system in such medical devices may be based on any of various suitable types of respiratory delivery systems which are suitable for administering a therapeutically effective dose of the polymer(s) of the present invention to a subject.

The inhalation device may be configured to deliver to the respiratory tract of the subject, preferably via the oral and/or nasal route, the compound in the form of an aerosol/spray, a vapor and/or a dry powder mist. Numerous respiratory systems and methods of incorporating therapeutic agents therein, such as the polymers of the present invention, suitable for assembly of a suitable inhalation device are widely employed by the ordinarily skilled artisan and are extensively described in the literature of the art (see, for example to U.S. Pat. Nos. 6,566,324, 6,571,790, 6,637,430, and 6,652,323; U.S. Food & Drug Administration (USFDA) Center For Drug Evaluation and Research (CDER); http://www.mece.ualberta.ca/arla/tutorial.htm).

The respiratory delivery system may thus be, for example, an atomizer or aerosol generator such as a nebulizer inhaler, a dry powder inhaler (DPI) and a metered dose inhaler (MDI), an evaporator such as an electric warmer and a vaporizer, and a respirator such as a breathing machine, a body respirator (e.g., cuirass), a lung ventilator and a resuscitator.

In still another embodiment of this aspect of the present invention, the medical device is such that delivering the polymer(s) is effected transdermally. In this embodiment, the medical device is applied on the skin of a subject, so as to transdermally deliver the polymer(s) to the blood system.

Exemplary medical devices for transdermally delivering a polymer according to the present invention include, without limitation, an adhesive plaster and a skin patch. Medical devices for transdermal or transcutaneous delivery of the polymer(s) typically further include one or more penetration enhancers, for facilitating their penetration through the epidermis and into the system.

According to another embodiment of this aspect of the present invention, the medical device is such that delivering the polymer(s) is effected by topically applying the medical device on a biological surface of a subject. The biological surface can be, for example, a skin, scalp, an eye, an ear and a nail. Such medical devices can be used in the treatment of various skin conditions and injuries, eye and ear infections and the like.

Exemplary medical devices for topical application include, without limitation, an adhesive strip, a bandage, an adhesive plaster, a wound dressing and a skin patch.

In another embodiment of this aspect of the present invention, the medical device is such that delivering the polymer(s) is effected by implanting the medical device in a bodily organ. As used herein, the term “organ” further encompasses a bodily cavity.

The organ can be, for example, a pulmonary cavity, a heart or heart cavity, a bodily cavity, an organ cavity, a blood vessel, an artery, a vein, a muscle, a bone, a kidney, a capillary, the space between dermal layers, an organ of the female or male reproductive system, an organ of the digestive tract and any other visceral organ.

The medical device according to this embodiment of the present invention typically includes a device structure in which a polymer according to the present invention is incorporated. The polymer(s) can thus be, for example, applied on, entrapped in or attached to (chemically, electrostatically or otherwise) the device structure.

The device structure can be, for example, metallic structure and thus may be comprised of a biocompatible metal or mixture of metals (e.g., gold, platinum).

Alternatively, the device structure may be comprised of other biocompatible matrices. These can include, for example, plastics, silicon, polymers, resins, and may include at least one component such as, for example, polyurethane, cellulose ester, polyethylene glycol, polyvinyl acetate, dextran, gelatin, collagen, elastin, laminin, fibronectin, vitronectin, heparin, segmented polyurethane-urea/heparin, poly-L-lactic acid, fibrin, cellulose and amorphous or structured carbon such as in fullerenes, and any combination thereof.

In cases where a biodegradable implantable device is desired, the device structure can be comprised of a biocompatible matrix that is biodegradable. Biodegradable matrices can include, for example, biodegradable polymers such as poly-L-lactic acid.

Optionally, the device structure may be comprised of biocompatible metal(s) coated with other biocompatible matrix.

Further optionally, in cases where a device which releases the polymer(s) of the present invention in a controlled manner is desired, the device structure can be comprised of or coated with a biocompatible matrix that functions as or comprises a slow release carrier. The biocompatible matrix can therefore be a slow release carrier which is dissolved, melted or liquefied upon implantation in the desired site or organ. Alternatively, the biocompatible matrix can be a pre-determined porous material which entraps the polymer(s) in the pores. When implanted in a desired site, the polymer(s) diffuse out of the pores, whereby the diffusion rate is determined by the pores size and chemical nature. Further alternatively, the biocompatible matrix can comprise a biodegradable matrix, which upon degradation releases the polymer(s) of the present invention.

The polymer(s) of the present invention can be incorporated in the device structure by any methodology known in the art, depending on the selected nature of the device structure. For example, the polymer(s) can be entrapped within a porous matrix, swelled or soaked within a matrix, or being adhered to a matrix.

Much like their antimicrobial activity in the body, the antimicrobial activity of the polymers of the present invention may further be harnessed for the preservation of food ingredients and products.

Hence, according to yet another aspect of the present invention there is provided a food preservative comprising an effective amount of the polymer of the present invention as described herein.

The polymer(s) may be incorporated into the food product as one of its ingredients either per se, or with an edible carrier.

The polymers of the present invention have been shown to have high and selecting affinity towards membranes of microorganisms as demonstrated in the Examples section that follows. This attribute is one of the main elements which contribute to the effective and efficacious activity of the polymers when utilized as an antimicrobial agent. When the polymer is coupled with a labeling agent, this membrane binding attribute can be further employed to label colonies and proliferation sites of microorganisms, especially microbial growth loci in a host in vivo.

Hence, according to another aspect of the present invention there is provided an imaging probe for detecting a pathogenic microorganism, the imaging probe comprising a polymer as defined and described hereinabove, whereas the polymer further includes at least one labeling agent, as defined hereinabove, attached thereto. When released to the environment, these polymers, having a labeling agent attached thereto will bind to the membrane of cell of microorganisms and therefore attach the labeling agent to the cells of the microorganism.

As used herein, the term “chromophore” refers to a chemical moiety that, when attached to another molecule, renders the latter colored and thus visible when various spectrophotometric measurements are applied.

The phrase “fluorescent compound” refers to a compound that emits light at a specific wavelength during exposure to radiation from an external source.

The phrase “phosphorescent compound” refers to a compound emitting light without appreciable heat or external excitation as by slow oxidation of phosphorous.

A heavy metal cluster can be for example a cluster of gold atoms used, for example, for labeling in electron microscopy techniques.

According to preferred embodiments of the present invention, one or more labeling agents may be attached to the polymer at any substitutable position, as in the case of an active agent discussed above. Examples of such substitutable positions are, without limitation, a side chain of any one or more of the amino acid residues in the polymer, any one of the linking moieties of the polymer, any one of the N- and C-termini of the polymer and any one or more of the hydrophobic moiety residues in the polymer.

Additional objects, advantages, and novel features of the present invention will become apparent to one ordinarily skilled in the art upon examination of the following examples, which are not intended to be limiting. Additionally, each of the various embodiments and aspects of the present invention as delineated hereinabove and as claimed in the claims section below finds experimental support in the following examples.

EXAMPLES

Reference is now made to the following examples, which together with the above descriptions; illustrate the invention in a non limiting fashion.

Materials and Experimental Methods Chemical Syntheses:

Materials:

Lysine having Fmoc ((9H-fluoren-9-yl)methyl carbonate) protection on its main-chain amine group and Boc (tert-butyl carbonate) protection on its side-chain amine group was purchased from Applied Biosystems and from NovaBiochem.

ω-amino fatty acids such as 4-amino-butyric acid, 8-amino-caprylic acid and 12-animo-lauric acid having Fmoc protection of the amine group were purchased from Sigma-Aldrich/NovaBiochem.

All other solvents and reagents used were purchased from Sigma-Aldrich/NovaBiochem/Applied Biosystems/J. T. Baker and were used without further purification.

Preparation of Libraries of Antimicrobial Polymers—General Procedure

The polymers according to the present invention were prepared by a solid phase method and were purified to chromatographic homogeneity according to methodologies described in the art (Feder, R. et al. (2000) J. Biol. Chem. 275, 4230-4238). Briefly, the polymers were synthesized by applying the Fmoc active ester chemistry on a fully automated, programmable peptide synthesizer (Applied Biosystems 433A). After cleavage from the resin, the crude polymers were extracted with 30% acetonitrile in water and purified to obtain a chromatographic homogeneity greater than 95%, as determined by HPLC (Alliance Waters).

HPLC chromatograms were performed on C18 columns (Vydak, 250 mm×4.6 or 10 mm) using a linear gradient of acetonitrile in water (1% per minute), both solvents contained 0.1% trifluoroacetic acid. The purified polymers were subjected to mass spectrometry (ZQ Waters) to confirm their composition and stored as a lyophilized powder at −20° C. Prior to being tested, fresh solutions were prepared in water, mixed by vortex, solubilized by ultrasound, centrifuged and then diluted in the appropriate medium.

In order to estimate the hydrophobicity of each polymer, the polymer was eluted with a linear gradient of acetonitrile (1% per minute) on an HPLC reversed-phase C18 column, and the percent of acetonitrile at which the polymer was eluted was used for hydrophobicity estimation (see, “ACN (%)” in Table 3 below).

Exemplary building units which were utilized in the synthesis described above are presented in Scheme 1 below and include: lysine and an ω-amino-fatty acid having m carbon atoms (Compound I).

Synthesis of exemplary polymers according to the present invention, which are comprised of lysine and Compound I, was performed by adding an Fmoc/Boc-protected lysine and an Fmoc-protected Compound I separately and sequentially to the resin according to conventional peptide solid phase synthesis protocols.

In Vitro Studies:

Bacterial Strains and Sample Preparation:

Antibacterial activity was determined using the following strains, cultured in LB medium (10 grams/liter trypton, 5 grams/liter yeast extract, 5 grams/liter NaCl, pH 7.4): Escherichia coli (ATCC (American Type Culture Collection) 35218); methicilin resistant Staphylococcus aureus (CI (clinical isolate) 15903); Bacillus cereus (ATCC 11778); and Pseudomonas aeruginosa (ATCC 9027).

Minimal Inhibitory Concentration (MIC) Measurements:

Minimal inhibitory concentrations (MICs) were determined by microdilution susceptibility testing in 96-well plates using inocula of 10⁶ bacteria per ml.

Cell populations were evaluated by optical density measurements at 600 nm and were calibrated against a set of standards. Hundred (100) μl of a bacterial suspension were added to 100 μl of culture medium (control) or to 100 μl of culture medium containing various polymer concentrations in 2-fold serial dilutions. Inhibition of proliferation was determined by optical density measurements after an incubation period of 24 hours at 37° C.

Alternatively, MICs were determined using the microbroth dilution assay recommended by the Clinical and Laboratory Standards Institute (CLSI) using two-fold serial dilutions in cation-adjusted Mueller-Hinton broth (CAMHB).

Clinical bacterial isolates were obtained from Tel Aviv Sourasky Medical Center, Israel. Bactericidal kinetics was assessed using the drop plate method [see, for example, Chen et al., Journal of Microbiological Methods, November; 55(2):475-9, 2003; and Skerman V. B. D., 1969, Abstracts of Microbiological Methods, p. 143-161, Wiley-Interscience, New York]. Statistical data for each experiment were obtained from at least two independent assays performed in duplicates.

The Effect of Physical Parameters (Charge and Hydrophobicity) on Antimicrobial Activity:

A library of polymers was prepared to sample the effect of increased charge and hydrophobicity on the antimicrobial activity. The charge was serially sampled by increasing the number of the ω-amino-fatty acid-lysine conjugates from 1 to 7. The hydrophobicity was serially sampled by increasing the number of the carbon atoms of the ω-amino fatty acid (4, 8 and 12). The polymers in each series were tested for their antimicrobial activity, as described hereinabove.

Development of Antimicrobial-Resistance in Bacteria:

The possible development of resistance to the antimicrobial activity of the polymers of the present invention by bacteria, as compared with known resistance-inducing classical antibiotic agents, gentamycin, tetracycline and ciprofloxacin, which served as controls for the development of antibiotic-resistant bacterial strains, was studied.

Bacteria samples (E. coli strain ATCC 35218) at the exponential phase of growth were exposed to an antimicrobial agent for MIC determination as described above. Following incubation overnight, bacteria were harvested from wells that displayed near 50% growth inhibition, washed and diluted in fresh medium, grown overnight, and subjected again to MIC determination for up to 15 iterations (15 days). For each compound tested, the 0D₆₂₀ of one half the MIC well from the previous MIC assay was diluted to yield 5×10⁵ cells/ml in LB (according to a calibration curve) and was used again for MIC determination in subsequent generations.

In parallel, MIC evolution in these subcultures was compared concomitantly with each new generation, using bacteria harvested from control wells (wells cultured without a polymer) from the previous generation. The relative MIC was calculated for each experiment from the ratio of MIC obtained for a given subculture to that obtained for first-time exposure.

Kinetic Studies:

The kinetic assays were performed in test tubes, in a final volume of 1 ml, as follows: 100 μl of a suspension containing bacteria at 2-4×10⁷ colony forming units (CFUs)/ml in culture medium were added to 0.9 ml of culture medium or culture medium containing various polymer concentrations (0, 3 and 6 multiples of the MIC value). After 0, 30, 60, 90, 120 and 360 minutes of exposure to the polymer at 37° C. while shaking, cultures were subjected to serial 10-fold dilutions (up to 10⁻⁶) by adding 50 μl of sample to 450 μl saline (0.9% NaCl). Colony forming units (CFUs) were determined using the drop plate method (3 drops, 20 μl each, onto LB-agar plates, as described in Yaron, S. et al. (2003), Peptides 24, 1815-1821). CFUs were counted after plate incubation for 16-24 hours at 37° C. Statistical data for each of these experiments were obtained from at least two independent assays performed in duplicates.

Antimicrobial Activity at Enhanced Outer-Membrane Permeability Conditions:

The outer membrane permeability of gram-negative bacteria, namely E. coli or P. aeruginosa, was enhanced by treating bacterial cultures with EDTA (ethylenediaminetetraacetic acid) according to the following procedure: 1 M EDTA solution in water (pH=8.3) was diluted in LB medium to obtain a 4 mM concentration and the diluted solution was used for polymer dissolution. Bacteria were grown overnight in LB medium, and 100 μl fractions containing 10⁶ bacteria per ml were added to 100 μl of EDTA culture medium or to EDTA culture medium containing various polymer concentrations (2-fold serial dilutions) in 96-well plates. Growth inhibition was determined against gram-negative bacteria as described above.

Susceptibility to Plasma Proteases:

The susceptibility of the polymers of the present invention to proteolytic digestion was assessed by determining the antibacterial activity after exposure to human plasma as follows: 250 μl of polymer solutions in saline (0.9% NaCl) at a concentration of 16 multiples of the MIC value were pre-incubated with 50% (v/v) human plasma in culture medium at 37° C. After incubation periods of 3, 6, and 18 hours, the polymer solutions were subjected to 2-fold serial dilutions in LB medium in 96-well plates. The susceptibility of the polymers of the present invention to enzymatic cleavage was assessed by pre-incubating four exemplary polymers according to the present invention, C₁₂K(NC₈K)₅NH₂, K(NC₁₂K)₃NH₂, C₁₂KNC₁₂KNH₂, and C₁₂KKNC₁₂KNH₂, and a 16-residues dermaseptin S4 derivative (S4₁₆, an exemplary AMP which served as the control), in human plasma (50%) for various time periods. The antibacterial activity was thereafter determined against E. coli and S. aureus, as described above. In parallel, antibacterial activity was also determined in culture medium conditions in the absence of plasma (referred to as 0 hours of pre-incubation in the experimental results section below). Statistical data was obtained from at least two independent experiments performed in duplicates.

Hemolysis Assays:

The polymer's membranolytic potential was determined against human red blood cells (RBC) in phosphate buffer solution (PBS). Human blood samples were rinsed three times in PBS by centrifugation for 2 minutes at 200×g, and re-suspended in PBS at 5% hematocrit. A 50 μl-fractions of a suspension containing 2.5×10⁸ RBC were added to test tubes containing 200 μl of polymer solutions (2-fold serial dilutions in PBS), PBS alone (for base-line values), or distilled water (for 100% hemolysis). After 3 hours incubation at 37° C. under agitation, samples were centrifuged, and hemolytic activity was determined as a function of hemoglobin leakage by measuring absorbance at 405 nm of 200 μl aliquots of the supernatants.

Alternatively, a 10% hematocrit was used and hemolysis was determined after one hour incubation. Hemolytic activity was determined according to Antibacterial Peptides Protocols as presented by Tossi, A. et al. in Methods Mol. Biol., 1997, 78, pp. 133-150.

Circular Dichroism (CD):

CD spectra in millidegrees were measured with an Aviv model 202 CD spectrometer (Aviv Associates, Lakewood, N.J.) using a 0.01 cm rectangular QS Hellma cuvette at 25° C. (controlled by thermoelectric Peltier elements with an accuracy of 0.1° C.). Polymer samples were dissolved in either PBS, 20% (v/v) trifluoroethanol/water or titrated in PBS containing POPC (2-oleoyl-1-palmitoyl-sn-glycero-3-phosphocholine) and POPG (1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-rac-(1-glycerol)) in a 3:1 ratio and concentration of up to 2 mM, to thereby obtain liposomes. CD spectra of the polymers were scanned at a concentration of 100 μM as determined by UV using standard curves of known concentrations for each polymer. The CD of the N-terminus acylated S4 dermaseptin derivative NC₁₂K₄S4(1-14) (Mor, A. et al. (1994), J. Biol. Chem. 269(50): 31635-41), an exemplary AMP, was measured under the same conditions and was used as a reference compound in the CD studies. The CD data presented herein represent an average of three separate recordings values.

Surface Plasmon Resonance Assay:

Binding to model bilayer membranes was studied by surface plasmon resonance (SPR) using a BIAcore 2000 biosensor system. Liposomes composed of phospholipids mimicking bacterial plasma membrane (POPC:POPG in a 3:1 ratio) were immobilized on the sensor surface and polymer solutions were continuously flowed over the membrane. The curve of resonance signal as a function of time displays the progress of the interaction between the analyzed polymer and the immobilized phospholipid membrane. The affinity of the interaction was calculated from analysis of the resulting curves as detailed in Gaidukov, L. et al. (2003), Biochemistry 42, 12866-12874. Briefly, the association and dissociation curves (binding rates) were analyzed at five doses (0.21, 0.42, 0.84, 1.67, 3.35 μg), and the K_(app) (the resulting binding constant) was calculated assuming a 2-step model).

Lipopolysaccharide Binding Assay:

In order to explore the mechanism by which the polymers of the present invention exert the anti-bacterial activity, the targeting of the polymers to the bacterial membrane was tested. More specifically, the binding affinity of the positively charged polymers to the negatively charged lipopolysaccharides (LPS) present on the membrane of gram-negative bacteria was tested.

Thus, binding assays of the polymers of the present invention to LPS were carried out with SPR technology using the optical biosensor system BIAcore 2000 (BIAcore). A mixture of 50 μM of the polymer samples in PBS and 100 μg/ml LPS was incubated for 30 minutes at room temperature. The binding assay was performed by injecting 10 μl of the mixture at a flow rate of 10 μl per minute at 25° C. over a POPC:POPG (3:1) bilayer spread on an L1 sensor chip. 100 μg/ml LPS without a polymer sample were injected as a blank of LPS binding to the membrane and 50 μM of a polymer sample was injected to determine the polymer binding to membrane without LPS.

DNA Binding Assay:

Binding of the polymers of the present invention to nucleic acids was studied by assessing their ability to retard migration of DNA plasmids during gel electrophoresis in a 1% agarose gel. DNA-retardation experiments were performed by mixing 200 nanograms of the plasmid DNA (pUC19, 2683 base pairs) with increasing amounts of various polymers in a final volume of 20 μl doubly distilled water (DDW). The reaction mixtures were incubated at room temperature for 30 minutes. Subsequently, 2 μl of loading dye (20% Ficoll 400, 0.1 M EDTA, 0.25% bromophenol blue and 1% sodium dodecyl sulfate) were added and an aliquot of 20 μl was applied to 1% agarose gel electrophoresis in TAE buffer (0.02 M Tris base, 0.01 M glacial acetic acid, 0.5 mM EDTA, pH=8.5) containing ethidium bromide (0.25 μg/ml). The plasmid used in this experiment was isolated by the Wizard® Plus SV Minipreps DNA Purification System (Promega).

Saliva Microbicidal Assays:

Antimicrobial activity of polymers of the present invention against the mélange of microorganisms in the saliva of healthy human volunteers was studied by mixing fresh human saliva with the polymers or IB-367 (both dissolved in 10 mM sodium acetate buffer set at pH 5 to a final concentration of 100 μM) at a 1:1 ratio. A solution of the saliva with no anti-bacterial agent served as a control. IB-367 is a positively charged protegrin peptide with known in-vitro and in-vivo activities against the microflora associated with human oral mucositis (Loury, D. et al., 1999, Oral Surg Oral Med Oral Pathol Oral Radiol Endod 87(5): 544-51.). Each of the solutions was spread over a LA plate, and the plated saliva samples were incubated overnight at 37° C. without aeration. The colonies were enumerated and counted to determine the microbicidal effect of the drug. The values of viable colony forming units (CFU) were determined as described above.

Anti-Malarial Assays:

The investigation of the anti-malarial activity of the polymers of the present invention was performed by screening part of the library of the polymers presented hereinbelow in Table 3, for anti-malarial and hemolytic activities as well as for their toxic activities against mammalian cells in culture.

Parasite cultivation: Different strains of P. falciparum were cultivated as described by Kutner and co workers [Kutner, S., Breuer, W. V., Ginsburg, H., Aley, S. B., and Cabantchik, Z. I. (1985) J. Cell. Physiol. 125, 521-527] using human red blood cells (RBC). The cultures were synchronized by the sorbitol method [Lambros, C. J., and Vanderberg, J. P. (1979) J. Parasitol. 65, 418-420] and infected cells were enriched from culture by Percoll-alanine gradient centrifugation [Kutner, S., Breuer, W. V., Ginsburg, H., Aley, S. B., and Cabantchik, Z. I. (1985) J. Cell. Physiol. 125, 521-527].

Determination of IC₅₀: Synchronized cultures at the ring stage were cultured at 1% hematocrit and 2% parasitemia in the presence of increasing concentrations of the tested polymers. After 18 hours of incubation parasite viability was determined by [³H]hypoxanthine (Hx) uptake (final concentration was 2 μCi/ml) during 6 hours and compared to controls (without the polymers). The 50% inhibitory concentration (IC₅₀) was determined by nonlinear regression fitting of the data using the commercially available software suite Sigmaplot™.

Time- and stage-dependence action of the polymers: Anti-malarial drugs are known to exert their action differentially on different stages of parasite development. They also need a minimal time of interaction with the parasite in order to inhibit its growth. Therefore, cultures at the ring stage were seeded in 24-well plate at 1% hematocrit, 2% parasitemia in plate medium (growth medium without hypoxanthine, 10 mM NaHCO3 and 7% heat inactivated human plasma). Tested polymers were added at different concentrations immediately and removed after 6, 24 and 48 hours. Cultures without polymers were left to mature to the trophozoite stage and dosed with compounds for 6 and 24 hours. Two μCi of Hx per well were added to all cells after 30 hours from the onset of the experiment and the cells were harvested after 24 hours.

Effect of the polymers on mammalian cells in culture: MDCK (cell line from dog kidney) epithelial cells were grown to confluence (about 3 days in culture). Parallel cultures were grown with different concentrations of the tested polymers. Thereafter 10 μl of Alamar blue was added and fluorescence was measured after 3.5 hours. For a positive control, 10 μM of cycloheximide were added to control samples at the beginning of cultivation.

In-Vivo Studies:

Activity Assay:

In-vivo prevention of E. coli-induced mortality using acute peritonitis and sepsis model experiments were conducted using female neutropenic ICR (Institute for Cancer Research) mice (weighing 25 to 27 grams each).

A bacterial inoculum was prepared on brain heart infusion (BHI) broth (Becton-Dickinson) with agitation (180 rpm) at 37° C. for 5 to 6 hours. Cells were harvested when the culture reached an optical density of 0.8 OD₆₂₀ and re-suspended in sterile BHI broth. The number of viable cells was verified by plating serial dilutions of the injected inocula onto BHI agar plates.

Infection was induced by intraperitoneal injection of 2.5×10⁶ or 5×10⁶ colony forming units (CFU) of E. coli in the logarithmic growth phase (CI-3504, isolated from a patient with peritonitis and bacteremia) in 0.5 ml of culture media to groups of 10 mice each. One hour after infection, mice were intraperitoneally injected with 0.5 ml of vehicle (PBS control), one 4 mg/kg body weight dose of an exemplary polymer, C₁₂K(NC₈K)₇NH₂, or 4 doses injection (after 1, 6, 20, and 28 hours) of 2 mg/kg body weight of imipenem (an antibiotic drug which belongs to the carbapenems family and used to treat severe or very resistant infections). Mice were monitored for survival over 6 days period after infection.

Toxicity:

Acute toxicity was examined after intraperitoneal injection of C₁₂K(NC₈K)₇NH₂, an exemplary polymer according to the present invention, to groups of 12 ICR mice. Each mouse was injected with a 0.5 ml solution of freshly prepared C₁₂K(NC₈K)₇NH₂ in PBS. The doses of polymer administered per mouse were 0 μg (blank control), 100 μg, 250 μg, and 500 μg (corresponding to 0 mg/kg, 4 mg/kg, 10 mg/kg, and 20 mg/kg body weight). Animals were directly inspected for adverse effects for 4 hour, and mortality was monitored for 7 days thereafter.

Experimental Results

Preparation of Libraries of Polymers:

Several representative series of polymers according to the present invention, which are substantially comprised of a plurality of lysine residues and ω-amino-fatty acid residues and fatty acid residues as hydrophobic moieties, were prepared according to the general procedure described above, and are presented in Table 3 below.

These exemplary polymers are referred to in this section according to the following formula:

T[NC_(i)K]_(j)G

In this formula, NC_(i) denotes an ω-amino-fatty acid residue (an exemplary hydrophobic moiety according to the present invention, represented by D₁ . . . Dn in the general formula I described herein), whereby i denotes the number of carbon atoms in the fatty acid residue; K denotes a lysine residue (an exemplary amino acid residue according to the present invention, denoted as A₁ . . . An in the general Formula I described herein, such that [NC_(i)K] denotes a residue of an ω-amino-fatty acid-lysine conjugate (denoted as [A₁-Z₁-D₁] . . . [An-Zn-Dn] in the general Formula I described herein); j denotes the number of the repeating units of a specific conjugate in the polymer (corresponding to n in the general Formula I described herein); and T and G each independently denotes either a hydrogen (no denotation), a lysine residue (denoted K), an ω-amino-fatty acid residue (denoted NC_(i)), a fatty acid residue (denoted C_(i)), an ω-amino-fatty acid-lysine conjugate residue (denoted NC_(i)K), a fluorenylmethyloxycarbonyl residue (denoted Fmoc), a benzyl residue (denoted Bz), a cholate residue (denoted Chl), an amine group (typically forming an amide at the C-terminus and denoted NH₂), and free acid residue (for the C-terminus no denotation), an alcohol residue, and any combination thereof (all corresponding to X and Y in the general formula I described herein).

Thus, for example, a polymer according to the present invention which is referred to herein as NC₁₂K(NC₈K)₇NH₂, corresponds to a polymer having the general formula I described hereinabove, wherein: X is a residue of a conjugate of an ω-amino-fatty acid having 12 carbon atoms (12-amino-lauric acid) and lysine; n is 6; A₁ . . . A₆ are each a lysine residue; D₁ . . . D₇ are all residues of an ω-amino-fatty acid having 8 carbon atoms (8-amino-caprylic acid); Z₁ . . . Z₇ and W₀—W₇ are all peptide bonds; and Y is an amine. For clarity, the chemical structure of NC₁₂K(NC₈K)₇NH₂ is presented in Scheme 2 below:

Minimal Inhibitory Concentration Measurements:

The polymers in each series were tested for various antimicrobial activities, as described hereinabove. The obtained results are presented in Table 3 below, wherein:

“Q” represents the overall molecular charge at physiological pH (column 3 in Table 3);

“ACN (%)” represents the percent of acetonitrile in the HPLC-RP gradient mobile phase at which the polymer was eluted and which corresponds to the estimated hydrophobicity of the polymer (column 4 in Table 3);

“LC50” represents the lytic concentration of each tested polymer in μM obtained by the membranolytic potential determination experiment of hemolysis of human red blood cells measured as described hereinabove (column 5 in Table 3);

“MIC E.c.” represents the minimal inhibitory concentration of each tested polymer in μM for E. coli, measured as described hereinabove in the antibacterial activity assay (column 6 in Table 3);

“MIC EDTA E.c.” represents the minimal inhibitory concentration of each tested polymer in μM for E. coli culture in the presence of 2 mM EDTA, measured as described hereinabove for the enhanced outer-membrane permeability assay (column 7 in Table 3);

“MIC P.a.” represents the minimal inhibitory concentration of each tested polymer in μM for P. aeruginosa, measured as described hereinabove for the antibacterial activity assay (column 8 in Table 3);

“MIC MR S.a.” represents the minimal inhibitory concentration of each tested polymer in μM for methicilin-resistant S. aureus, measured as described hereinabove for the antibacterial activity assay of antibiotic-resistant bacteria (column 9 in Table 3);

“MIC B.c.” represents the minimal inhibitory concentration of each tested polymer in μM for Bacillus cereus, measured as described hereinabove for the antibacterial activity assay (column 10 in Table 3); and

ND denotes “not determined”.

Some values are presented with ±standard deviations from the mean.

“Orn” and “Arg” in entries 84 and 85 denote ornithine and arginine amino acid residues respectively.

Entries 96 to 99 present activity data of four control antimicrobial peptides, namely MSI-78, a magainin derivative; IB-367, a protegrin derivative; K₄S₄(1-16), a dermaseptin derivative; and LL37, a cathelicidin derivative.

Entries 100 to 103 present activity data of four control antibiotic agents, namely Ciprofloxacin, Imipenem, Tetracycline and Rifampin.

TABLE 3 ACN MIC MIC MIC MIC MIC No. Polymer Q (%) LC50 E. c. EDTA E. c. P. a. MR S. a. B. c. 1 C₄KNC₄KNH₂ 2 19.6 >100 >50 ND >50 >50 >50 2 C₄K(NC₄K)₂NH₂ 3 21.8 >100 >50 ND >50 >50 >50 3 C₄K(NC₄K)₃NH₂ 4 21.5 >100 >50 ND >50 >50 >50 4 C₄K(NC₄K)₄NH₂ 5 22 >100 >50 ND >50 >50 >50 5 C₄K(NC₄K)₅NH₂ 6 22.9 >100 >50 ND >50 >50 >50 6 C₄K(NC₄K)₆NH₂ 7 23.5 >100 >50 ND >50 >50 >50 7 C₄K(NC₄K)₇NH₂ 8 24.3 >100 >50 ND >50 >50 >50 8 KNC₄KNH₂ 3 0 ND >50 ND >50 >50 >50 9 K(NC₄K)₂NH₂ 4 9 ND >50 ND >50 >50 >50 10 K(NC₄K)₃NH₂ 5 18.8 ND >50 ND >50 >50 >50 11 K(NC₄K)₄NH₂ 6 20.1 ND >50 ND >50 >50 >50 12 K(NC₄K)₅NH₂ 7 20.8 ND >50 ND >50 >50 >50 13 K(NC₄K)₆NH₂ 8 21.7 ND >50 ND >50 >50 >50 14 K(NC₄K)₇NH₂ 9 22.2 ND >50 ND >50 >50 >50 15 C₁₂K(NC₄K)₁NH₂ 2 50.2 ND >50 ND >50 >50 >50 16 C₁₂K(NC₄K)₂NH₂ 3 47.6 ND >50 ND >50 >50 >50 17 C₁₂K(NC₄K)₃NH₂ 4 46.4 ND >50 ND >50 >50 >50 18 C₁₂K(NC₄K)₄NH₂ 5 45.4 ND 50 ND >50 >50 >50 19 C₁₂K(NC₄K)₅NH₂ 6 45.8 ND 12.5 6.3 >50 >50 >50 20 C₁₂K(NC₄K)₆NH₂ 7 45.1 ND 9.4 ± 3.1 4.7 ± 2.2 >50 >50 >50 21 C₁₂K(NC₄K)₇NH₂ 8 45.2 >100 9.4 ± 3.1 3.1 >50 >50 >50 22 NC₁₂K(NC₄K)₅NH₂ 7 29.3 ND >50 ND >50 >50 >50 23 NC₁₂K(NC₄K)₆NH₂ 8 29.8 ND >50 ND >50 >50 >50 24 NC₁₂K(NC₄K)₇NH₂ 9 30.2 ND >50 ND >50 >50 >50 25 C₈KNC₈KNH₂ 2 38.9 >100 >50 ND >50 >50 >50 26 C₈K(NC₈K)₂NH₂ 3 36 >100 >50 ND >50 >50 >50 27 C₈K(NC₈K)₃NH₂ 4 39.5 >100 >50 ND >50 >50 >50 28 C₈K(NC₈K)₄NH₂ 5 40.5 >100 >50 ND >50 >50 >50 29 C₈K(NC₈K)₅NH₂ 6 40.8 >100 25 3.1 >50 >50 >50 30 C₈K(NC₈K)₆NH₂ 7 40.3 >100 25 ND >50 >50 >50 31 C₈K(NC₈K)₇NH₂ 8 40.3 >100 12.5 ND >50 >50 >50 32 KNC₈KNH₂ 3 21.6 ND >50 ND >50 >50 >50 33 K(NC₈K)₂NH₂ 4 27.3 ND >50 ND >50 >50 >50 34 K(NC₈K)₃NH₂ 5 30 ND >50 ND >50 >50 >50 35 K(NC₈K)₄NH₂ 6 31.7 ND >50 ND >50 >50 >50 36 K(NC₈K)₅NH₂ 7 33.1 ND >50 >50 >50 >50 >50 37 K(NC₈K)₆NH₂ 8 33.4 ND >50 >50 >50 >50 >50 38 K(NC₈K)₇NH₂ 9 34.2 ND >50 37.5 >50 >50 >50 39 C₁₂KNC₈KNH₂ 2 50.9 ND >50 ND >50 >50 >50 40 C₁₂K(NC₈K)₂NH₂ 3 48 ND >50 ND >50 >50 >50 41 C₁₂K(NC₈K)₃NH₂ 4 46 ND >50 ND >50 >50 >50 42 C₁₂K(NC₈K)₄NH₂ 5 49 ND 25 4.7 ± 2.2 >50 37.5 ± 18 50 43 C₁₂K(NC₈K)₅NH₂ 6 49.7 >100 3.1 0.4 50 50 12.5 44 C₁₂K(NC₈K)₆NH₂ 7 50 >100 3.1 0.8 50 50 12.5 45 C₁₂K(NC₈K)₇NH₂ 8 47.5 >100 3.1 ND 6.2 50 12.5 46 NC₁₂KNC₈KNH₂ 3 29.6 ND >50 ND >50 >50 >50 47 NC₁₂K(NC₈K)₂NH₂ 4 35 ND >50 ND >50 >50 >50 48 NC₁₂K(NC₈K)₃NH₂ 5 33.7 ND >50 ND >50 >50 >50 49 NC₁₂K(NC₈K)₄NH₂ 6 36.2 ND >50 12.5 >50 >50 >50 50 NC₁₂K(NC₈K)₅NH₂ 7 36.6 ND 50 6.3 >50 >50 >50 51 NC₁₂K(NC₈K)₆NH₂ 8 37 ND 25 6.3 >50 >50 >50 52 NC₁₂K(NC₈K)₇NH₂ 9 36.9 ND 12.5 ND 50 >50 >50 53 C₁₂KK(NC₈K)₄NH₂ 6 47 >100 6.3 ND 50 37.5 ± 18   25 54 C₁₂KNC₁₂KNH₂ 2 59 45 ± 12 20.8 ± 7.2  ND 50 18.8 ± 7.2  >50 55 C₁₂K(NC₁₂K)₂NH₂ 3 52.9 ND >50 37.5 ± 18   >50 >50 >50 56 C₁₂K(NC₁₂K)₃NH₂ 4 53.5 ND >50 >50 >50 >50 >50 57 C₁₂K(NC₁₂K)₄NH₂ 5 53.4 ND >50 >50 >50 >50 >50 58 KNC₁₂KNH₂ 3 32 >100 >50 >50 >50 >50 >50 59 K(NC₁₂K)₂NH₂ 4 40 >100 >50 >50 >50 >50 >50 60 K(NC₁₂K)₃NH₂ 5 44 >100 12.5 3.1 25 >50 >50 61 K(NC₁₂K)₄NH₂ 6 46 6.5 ± 3.5 25 2.3 ± 1.1 >50 >50 >50 62 K(NC₁₂K)₅NH₂ 7 47 ND >50 3.1 ND >50 >50 63 K(NC₁₂K)₆NH₂ 8 48 ND >50 3.1 ND ND >50 64 K(NC₁₂K)₇NH₂ 9 50 ND >50 6.3 ND ND >50 65 (NC₁₂K)₂NH₂ 3 38.8 >100 >50 >50 >50 >50 >50 66 (NC₁₂K)₃NH₂ 4 44.3 >100 25 6.3 50 >50 >50 67 (NC₁₂K)₄NH₂ 5 46.8   4 ± 1.4 >50 6.3 >50 >50 >50 68 (NC₁₂K)₅NH₂ 6 47.8 ND >50 12.5 >50 >50 >50 69 (NC₁₂K)₆NH₂ 7 49 ND >50 3.1 ND >50 ND 70 (NC₁₂K)₇NH₂ 8 50 ND >50 12.5 ND ND ND 71 (NC₁₂K)₈NH₂ 9 51 ND >50 1.6 ND ND ND 72 KKNC₁₂KNH₂ 4 30.9 >100 >50 ND >50 >50 >50 73 (KNC₁₂K)₂NH₂ 5 38.1 >100 >50 ND 50 >50 >50 74 K(KNC₁₂K)₂NH₂ 6 37.3 >100 >50 ND 25 >50 >50 75 C₈KKNC₁₂KNH₂ 3 40.3 >100 >50 ND >50 >50 >50 76 C₈(KNC₁₂K)₂NH₂ 4 45 >100 25 ND 12.5 >50 3.1 77 C₈K(KNC₁₂K)₂NH₂ 5 42.6 >100 37.5 ± 18   ND 12.5 >50 6.3 78 C₁₂KKNC₁₂KNH₂ 3 54 28.5 ± 9.2  18.8 ± 8.8  9.4 ± 4.4 25 3.1 3.1 79 C₁₂(KNC₁₂K)₂NH₂ 4 53.3 16.5 ± 6.4  3.1 ND 3.1 1.6 3.1 80 C₁₂K(KNC₁₂K)₂NH₂ 5 51 88 ± 3  3.1 ND 3.1 12.5 3.1 81 NC₁₂KKNC₁₂KNH₂ 4 38.9 >100 >50 ND >50 >50 >50 82 NC₁₂(KNC₁₂K)₂NH₂ 5 38.5 >100 50 ND 12.5 >50 3.1 83 NC₁₂K(KNC₁₂K)₂NH₂ 6 38.6 >100 25 ND 25 >50 6.3 84 C₁₂OrnNC₁₂OrnNH₂ 2 53.8 24 ± 6  10.4 ± 3.6  ND 25 12.5 16.7 ± 7.2  85 C₁₂ArgNC₁₂ArgNH₂ 2 57.1 9.5 ± 1     42 ± 14.4 ND >50 12.5   42 ± 14.4 86 C₁₂KNC₁₂K 1 56.9 >100 >50 ND >50 >50 >50 87 C₁₂K(NC₁₂K)₂ 2 56.4 ND >50 ND >50 31.3 ± 26.5 50 88 C₁₂K(NC₁₂K)₃ 3 54.6 ND >50 ND >50 >50 >50 89 KNC₁₂K 2 33.2 >100 >50 ND >50 >50 >50 90 K(NC₁₂K)₂ 3 36.4 >100 >50 ND >50 >50 >50 91 K(NC₁₂K)₃ 4 42.8 >100 25 ND 50 >50 >50 92 (NC₁₂K)₂ 2 38.7 >100 >50 ND >50 >50 >50 93 (NC₁₂K)₃ 3 43.8 >100 50 ND >50 50 >50 94 (NC₁₂K)₄ 4 45.8 ND 50 ND >50 >50 >50 95 FmocK(NC₁₂K)₂ 2 41 ND >50 ND >50 6.3 12.5 96 MSI-78 10 44 45 50 ND 3.1 >50 37.5 97 IB-367 5 45 7 3.1 ND 12.5 3.1 ND 98 K₄S₄(1-16) 6 47 10 3.1 ND 6.3 6.3 3.1 99 LL37 11 61 8 50 ND 12.5 ND 37.5 100 Ciprofloxacin ND ND ND 0.05 ND 0.3 >50 0.3 101 Imipenem ND ND ND 0.6 ND 16.4 >50 <0.03 102 Tetracycline ND ND ND 1.8 ND >50 0.4 0.07 103 Rifampin ND ND ND 7.7 ND 15.2 0.006 0.09

The Effect of Physical Parameters (Charge and Hydrophobicity) on Antimicrobial Activity:

Charge and hydrophobicity may be viewed as two conflicting physical characteristics of a molecule: charge facilitates dissolution of a compound in aqueous media by interacting with the polar water molecules, while hydrophobicity, which typically corresponds to the number and length of non-polar hydrocarbon moieties, hinders dissolution. Optimization of these physical characteristics is crucial in the development of drugs in general and antimicrobial agents in particular, as these characteristics affect pharmaceutically important traits such as membrane permeability and transport in and across biological systems.

Therefore, the library of polymers prepared to study the effect of serial increases in charge and hydrophobicity properties was measured for its antimicrobial activity against two gram-negative bacteria: E. coli (results are presented in column 6 of Table 3 hereinabove) and P. aeruginosa (results are presented in column 8 of Table 3), and two gram-positive bacteria: methicilin-resistant S. aureus (results are presented in column 9 of Table 3) and Bacillus cereus (results are presented in column 10 of Table 3).

A serial increase in positive charge was achieved by preparing polymers with serial elongation of the chain with respect to the number of lysine residues. Serial increases in hydrophobicity was achieved by preparing polymers with serial rising of the number of fatty acid residues (as a representative hydrophobic moiety) and/or with serial rising of the number of carbon atoms in each fatty acid residue. Serial increases in both positive charge and hydrophobicity were achieved by preparing polymers with serial rising of the number of lysine-amino fatty acid conjugates.

As can be seen in Table 3, increasing the hydrophobicity of the polymers by increasing the number of the carbon atoms in the fatty acid residue from 4 to 12, via 8 carbon atoms, was found to affect the antimicrobial activity of the polymers. Series of polymers in which the repeating hydrophobic moiety was a 4-amino-butyric acid (see, entries 1-24 in Table 3) was compared to a series in which the repeating hydrophobic moiety was an 8-amino-caprylic acid (see, entries 25-53 in Table 3) and to a series in which the repeating hydrophobic moiety was a 12-amino-lauric acid (see, entries 54-95 in Table 3). The results, presented in Table 3, indicated that polymers in which the repeating hydrophobic moiety was a 4-amino-butiric acid (see, entries 1-14 in Table 3) and a 8-amino-caprylic acid (see, entries 25-38 in Table 3), generally did not show significant antimicrobial activity up to the highest tested concentration of 50 μM. The only polymers which had no 12-animo-lauric acid residue in their sequence and which showed significant antimicrobial activity at lower concentrations were C₈K(NC₈K)₅NH₂, C₈K(NC₈K)₆NH₂ and C₈K(NC₈K)₇NH₂ (see, entries 29-31 in column 6 of Table 3), whereas polymers containing one or more of the more hydrophobic 12-amino-lauric acid residue, (see, entries 58-83 in Table 3), showed significant activity at concentrations as low as 16 μM.

Evaluation of the effect of the hydrophobicity of the polymers in terms of the acetonitrile percentages of the HPLC mobile phase in which the polymers were eluted further demonstrates the correlation between this property and the antimicrobial activity of the polymer. As can be seen in the data presented in column 4 of Table 3, all the polymers which displayed a significant level of antimicrobial activity against any one of the tested bacteria were eluted in acetonitrile concentrations higher than 36%, whereby none of the polymers that were eluted in acetonitrile concentrations lower than 36% exhibited such an activity.

FIG. 1 presents the distribution of polymers which exhibited a significant microbial activity (MIC value of less than 50 μM) in any one of the four assays conducted. As is clearly seen in FIG. 1, antimicrobial activity against one or more of the tested bacteria was exhibited only by polymers which were eluted at acetonitrile concentrations of 36% and up and, furthermore, polymers which were found active against all the tested bacteria were eluted at acetonitrile concentrations of 51% and up.

As can further be seen in Table 3, increasing the positive charge of the polymers by increasing the number of the lysine residues in the polymer was found to affect the antimicrobial activity of the polymers only marginally. Thus, polymers having net charges raging from +1 to +9 in each series were tested for antimicrobial activity. The results, presented in Table 3, indicated, for example, that most of the polymers with the highest net positive charge of +9, namely K(NC₄K)₇NH₂, NC₁₂K(NC₄K)₇NH₂, K(NC₈K)₇NH₂, NC₁₂K(NC₈K)₇NH₂, K(NC₁₂K)₇NH₂, (NC₁₂K)₈NH₂, (see, respective entries 14, 24, 38, 52, 64 and 71 in Table 3), did not exhibit significant activity, with only NC₁₂K(NC₈K)₇NH₂ (see, entry 52 in Table 3) exhibiting significant activity.

As can be concluded from the data presented in Table 3, while none of the polymers series based on hydrophobic moieties containing 4-carbon chains inhibited bacterial proliferation, three polymers from the polymers series based on hydrophobic moieties containing 8-carbon chains inhibited growth of E. coli, displaying MIC values in the low micromolar (μg/ml) range. Several observations stem from the results shown in Table 3: the equivalent 4-carbon chain based polymers, whose hydrophobicity values, represented by the percent of acetonitrile in the HPLC-RP gradient mobile phase at which the polymer was eluted and which corresponds to the estimated hydrophobicity of the polymer, varied between 20% and 25% (indicating low hydrophobicity) had virtually no antibacterial activity up to the highest concentration assayed (MIC>50 μM). The more hydrophobic 8-carbon chain based polymers became active only when they reached hydrophobicity values of >40% (see, C₈K(NC₈K)₅NH₂, entry 29 in Table 3). Elongating the polymer by one C₈K subunit (see, C₈K(NC₈K)₆NH₂, entry 30 in Table 3) increased the charge without significant change to hydrophobicity and did not alter activity. Further addition of another C₈K subunit (see, C₈K(NC₈K)₇NH₂, entry 31 in Table 3) had similar charge and hydrophobicity effects but led to a two-fold enhanced activity.

Overall, these results indicate that an optimal antibacterial activity emerges when a polymer, as described herein, attains an optimal window of charge and hydrophobicity, much as observed with conventional AMPs.

Table 4 below presents a summary of the results obtained in these experiments, in terms of the effect of the net positive charge of the polymers and the antimicrobial activity thereof. Row 2 of Table 4 presents the number of polymers in 9 bins, wherein each bin represents a net positive charge, starting from +9 to +1. Row 3 of Table 4 presents the total number of activity assays which were measured in the charge bin, namely, the number of polymers in the bin multiplied by the four bacterial assays described above. Row 4 of Table 4 presents the number of polymers in each of the bins that were found active against any one of the four bacteria. Row 5 of Table 4 presents the percentage of the active polymers from the total number of assays measured in the charge bin. As can be seen in Table 4, (row 4, for example), only a little if any correlation between the net positive charge of the polymers and their antimicrobial activity was found. It appears from these results that the only feature that seems to affect the antimicrobial activity of the tested polymers is a net positive charge that is greater than +1.

TABLE 4 Charge +9 +8 +7 +6 +5 +4 +3 +2 +1 Number of polymers 6 10 10 12 14 16 15 11 1 Number of assays 24 40 40 48 56 64 60 44 4 Number of actives 1 6 4 12 13 9 4 12 0 Percent actives 4.2% 15.0% 10.0% 25.0% 23.2% 14.1% 6.7% 27.3% 0.0%

FIG. 2 presents the distribution of polymers according to the present invention which exhibited a significant microbial activity (MIC value of less than 50 μM) in any one of the four assays mentioned above. As can be clearly seen in FIG. 2, polymers which showed antimicrobial activity against any one of the four bacteria are scattered across the entire range of charge values, excluding the +1 charge, and thus demonstrating the lack of correlation between the net positive charge of the polymers and the antimicrobial activity thereof.

Overall, these results indicated that antibacterial activity emerged when a polymer attained an optimal window of charge and hydrophobicity, much as observed with conventional AMPs. These results also suggested that a parallel increase in hydrophobicity value might enhance potency.

Antimicrobial Activity Against Gram-Negative Bacteria

The activity of the novel polymers describes herein on Gram-negative bacteria has also been tested. To date, new antimicrobial agents that are effective against Gram-negative bacteria are rarely found.

Table 5 below presents the results obtained in this study, and clearly shows that C₁₂K(NC₈K)₇NH₂, an exemplary polymer as presented herein, displayed potent growth inhibitory activity against 9 strains out of a panel of 10 Gram-negative bacterial strains.

“MIC” (column 3 in Table 5) represents the minimal inhibitory concentration of the exemplary polymer C₁₂K(NC₈K)₇NH₂ in μM for each of the tested bacterial strains, which induced 100% inhibition of proliferation after 24 hours incubation. Values represent the mean from two independent experiments performed in duplicates.

As can be seen in Table 5, the MIC observed for C₁₂K(NC₈K)₇NH₂ ranged from 1.6 μM to 12.5 μM and in general the MIC value for most bacterial strains was equal or inferior to 6.2 μM (14 μg/ml). These encouraging results were also observed for clinically challenging species such as Acinetobacter and Pseudomonas, for both of which a MIC value of 3.1 was observed (see, entries 5 and 6 in Table 5 respectively).

TABLE 5 Entry Gram-negative Bacteria Strain MIC 1 Enterobacter cloacae CI 730 1.6 2 Brevundimonas diminuta ATCC 19146 1.6 3 Yersinia kristensenii ATCC 33639 1.6  4a Escherichia coli CI 3504 1.6*  4b Escherichia coli ATCC 25922 3.1* 5 Acinetobacter baumanii CI 1280 3.1 6 Klebsiella pneumoniae CI 1286 3.1 7 Proteus mirabilis CI 1285 6.2 8 Pseudomonas aeruginosa CI 8732 6.2 9 Stenotrophomonas CI 746 12.5 maltophilia 10  Serratia odorifera ATCC 33077 >50 *MIC determined using the Clinical and Laboratory Standards Institute (CLSI) recommended procedure as presented hereinabove.

Development of Antimicrobial-Resistance in Bacteria:

The possible development of resistance to the polymers of the present invention was tested by measuring the MIC levels following multiple exposures of the bacteria to exemplary polymers according to the present invention, as described hereinabove in the Experimental Methods section. The tested polymers in these experiments were K(NC₁₂K)₃NH₂, C₁₂K(NC₈K)₅NH₂, C₁₂KKNC₁₂KNH₂ and C₁₂K(NC₈K)₇NH₂, whereby the development of resistance of E. coli to K(NC₁₂K)₃NH₂ and C₁₂K(NC₈K)₅NH₂ was compared with that of three classical antibiotics: gentamycin, tetracycline and ciprofloxacin, the development of resistance of methicilin-resistant S. aureus to C₁₂KKNC₁₂KNH₂ was compared with that of two classical antibiotics: rifampicin and tetracycline, and the development of resistance of E. coli to C₁₂K(NC₈K)₇NH₂, evaluated during 15 serial passages, was compared with that of three classical antibiotics, ciprofloxacin, imipenem, and tetracycline.

The data obtained in these experiments is presented in FIGS. 3 a, 3 b and 3 c. FIG. 3 a presents the data obtained for K(NC₁₂K)₃NH₂ and C₁₂K(NC₈K)₅NH₂, FIG. 3 b presents the data obtained for C₁₂KKNC₁₂KNH₂ and FIG. 3 c presents the data obtained for C₁₂K(NC₈K)₇NH₂.

As is clearly seen in FIG. 3 a, the relative MIC value of K(NC₁₂K)₃NH₂ and C₁₂K(NC₈K)₅NH₂ against E. coli remained stable for 10 successive subculture generations following the initial exposure. In sharp contrast, during the same period of time, the MIC values tested with the reference antibiotic agents substantially increased, reflecting the emergence of antibiotic-resistant bacteria. Thus, at the tenth generation, the MIC values increased by 4-fold for tetracycline and gentamycin, and by more than 16-fold for ciprofloxacin. These results demonstrate that exposing bacteria to the antimicrobial polymers of the present invention do not result in development of resistance.

As is clearly seen in FIG. 3 b, the relative MIC value of C₁₂KKNC₁₂KNH₂ against methicilin-resistant S. aureus remained stable for 15 successive subculture generations following the initial exposure. In sharp contrast, during the same period of time, the MIC values tested with the reference antibiotic agents substantially increased, reflecting the emergence of antibiotic-resistant bacteria. Thus, at the fifteenth generation, the MIC values increased by more than 230-fold for rifampicin, and by 4-fold for tetracycline. These results demonstrate again that exposing bacteria to the antimicrobial polymers of the present invention do not result in development of resistance.

Similarly, it can be seen in FIG. 3 c, the relative MIC value of C₁₂K(NC₈K)₇NH₂ against E. coli remained stable for 15 successive subculture generations following the initial exposure. In sharp contrast, during the same period of time, the MIC values tested with the reference antibiotic agents substantially increased, reflecting the emergence of antibiotic-resistant bacteria. Thus, at the fifteenth generation, the MIC values increased by more than 60-fold for ciprofloxacin, and by 8-fold for imipenem and tetracycline. These results demonstrate yet again that exposing bacteria to the antimicrobial polymers of the present invention do not result in development of resistance.

The development of antimicrobial resistance following exposure to the polymers of the present invention was further evaluated in a cross resistance experiment, in which a methicilin-resistant strain of S. aureus was exposed to exemplary polymers of the present invention. The results obtained in this experiment are presented in Table 3 hereinabove, under column “MIC MR S.a.” and clearly demonstrate the persisting antimicrobial activity of the polymers of the present invention against an antibiotic-resistant bacteria, especially in the case of C₁₂(KNC₁₂K)₂NH₂, C₁₂KKNC₁₂KNH₂, FmocK(NC₁₂K)₂, C₁₂K(KNC₁₂K)₂NH₂, C₁₂OrnNC₁₂OrnNH₂, C₁₂ArgNC₁₂ArgNH₂, C₁₂KNC₁₂KNH₂, C₁₂K(NC₁₂K)₂, C₁₂K(NC₈K)₄NH₂ and C₁₂KK(NC₈K)₄NH₂ (see, respective entries 79, 78, 95, 80, 84, 85, 54, 87, 42 and 53, in Table 3).

Kinetic Studies of Antimicrobial Activity at Time Intervals:

The kinetic rates of bactericidal activity of a representative polymer of the present invention, C₁₂K(NC₈K)₅NH₂, was tested as described in the methods section above at concentrations corresponding to 3 and 6 times the MIC value. The results, presented in FIG. 4, clearly reflect the antibacterial activity of the polymer. As is shown in FIG. 4, the viable bacterial population was reduced by nearly seven log units within 6 hours upon being exposed to the polymer at a concentration of 3 multiples of the MIC, and within 2 hours upon being exposed to the polymer at a concentration of 6 multiples of the MIC.

FIG. 5 presents comparative plots demonstrating the kinetic bactericidal effect of C₁₂K(NC₈K)₇NH₂, an exemplary polymer according to the present invention, on E. coli. as compared with kinetic bactericidal effect of various classical antibiotics as determined at a concentration corresponding to six multiples of their respective MIC value.

As can be seen in FIG. 5, C₁₂K(NC₈K)₇NH₂, (black triangles) was responsible for rapid bacterial death namely, C₁₂K(NC₈K)₇NH₂ reduced bacterial population from 106 to <50 CFU/ml within one hour compared to normal bacterial growth control (black circles), while Imipenem (white squares) and Ciprofloxacin (black squares) induced a weaker bactericidal effect, and Tetracycline (white circles) was merely bacteriostatic. The plotted values represent the mean±standard deviations obtained from at least two independent experiments. The stared datum points indicate that bacteria were not detected at the minimum level of sensitivity (<50 CFU/ml).

These remarkable results further demonstrate the efficacy of the antimicrobial polymers of the present invention, in terms of an efficient pharmacokinetic profile.

Antimicrobial Activity at Enhanced Outer-Membrane Permeability Conditions:

The results obtained following addition of the cation-chelator EDTA to the assay buffer, which was aimed at enhancing the outer-membrane permeability of gram-negative bacteria such as E. coli, are presented in Table 3 above under the column headed “MIC EDTA E.c.”. These results clearly show that the activity profile of the polymers in the presence of EDTA is different than that obtained without EDTA (presented in Table 3 above, column headed “MIC E.c.”). Thus, polymers such as K(NC₈K)₇NH₂, NC₁₂K(NC₈K)₄NH₂, NC₁₂K(NC₈K)₅NH₂, C₁₂K(NC₁₂K)₂NH₂, K(NC₂K)₅NH₂, K(NC₁₂K)₆NH₂, K(NC₂K)₇NH₂, (NC₁₂K)₄NH₂, (NC₁₂K)₅NH₂, (NC₁₂K)₆NH₂, (NC₁₂K)₇NH₂ and (NC₁₂K)₈NH₂, which exhibited minor or no antimicrobial activity in the absence of EDTA, became up to more than 50 folds more active in its presence (see, respective entries 38, 49, 50, 55, 62, 63, 64, 67, 68, 69, 70 and 71, in Table 3). Other polymers, such as K(NC₁₂K)₄NH₂, C₈K(NC₈K)₅NH₂, C₁₂K(NC₈K)₄NH₂, NC₁₂K(NC₈K)₆NH₂ and (NC₁₂K)₃NH₂, which exhibited only marginal antimicrobial activity in the absence of EDTA, became between 11-folds and 4-fold more active in its presence, respectively (see, respective entries 61, 29, 42, 51 and 66 in Table 3).

These results illuminate the tight correlation between membrane permeability of antimicrobial agents and their efficacy and further demonstrate the complex relationship and delicate balance between the positive charge and the hydrophobic characteristics of the polymers of the present invention on the antimicrobial activity thereof.

Susceptibility to Plasma Proteases Assays Results:

The susceptibility of the polymers of the present invention to enzymatic cleavage was assessed by pre-incubating exemplary polymers according to the present invention, C₁₂K(NC₈K)₅NH₂, K(NC₁₂K)₃NH₂, C₁₂KNC₁₂KNH₂, and C₁₂KKNC₁₂KNH₂, and an exemplary reference AMP, a 16-residues dermaseptin S4 derivative (S4₁₆), in human plasma (50%) for various time periods and thereafter determining the antibacterial activity thereof against E. coli and S. aureus. Statistical data were obtained from at least two independent experiments performed in duplicates.

The results are presented in Table 6 hereinbelow, wherein “MIC (E.c.) C₁₂K(NC₈K)₅NH₂ (μM)” is the minimal inhibitory concentration in μM of C₁₂K(NC₈K)₅NH₂, as measured for E. coli; “MIC (E.c.) K(NC₁₂K)₃NH₂ (μM)” is the minimal inhibitory concentration in μM of K(NC₁₂K)₃NH₂, as measured for E. coli; “MIC (E.c.) S4₁₆ (μm)” is the minimal inhibitory concentration in μM of S4₁₆, an exemplary dermaseptin serving as a reference AMP, as measured for E. coli; “MIC S.a. C₁₂KNC₁₂KNH₂ (μM)” is the minimal inhibitory concentration in μM of C₁₂KNC₁₂KNH₂, as measured for S. aureus; and “MIC (S.a.) C₁₂KKNC₁₂KNH₂ (μM)” is the minimal inhibitory concentration in μM of C₁₂KKNC₁₂KNH₂, as measured for S. aureus.

TABLE 6 Incubation MIC (E.c.) MIC (E.c.) MIC MIC (S.a.) MIC (S.a.) time C₁₂K(NC₈K)₅NH₂ K(NC₁₂K)₃NH₂ (E.c.) S4₁₆ C₁₂KNC₁₂KNH₂ C₁₂KKNC₁₂KNH₂ (hours) (μM) (μM) (μM) (μM) (μM) 0 3.1 12.5 3.1 12.5 3.1 3 3.1 12.5 >50 12.5 3.1 6 3.1 12.5 >50 25 6.3 18 3.1 12.5 >50 25 6.3

As is shown in Table 6, while the reference AMP, S4₁₆, was completely inactivated upon exposure to human plasma, the polymers of the present invention maintained their activity, and thus, the superior stability of the polymers according to the present invention as compared with that of the highly active yet unstable AMPs was clearly demonstrated. More specifically, as is shown in Table 6, the dermaseptin S4₁₆ did not display a measurable MIC after 3 hours exposure to serum enzymes, even at a concentration of more than 16-folds higher (greater than 50 μM) than the MIC value, indicating that the peptide was inactivated probably due to enzymatic proteolysis.

In sharp contrast, the polymers of the present invention exhibited prolonged resistance to enzymatic degradation. As is further shown in Table 6, the activity of short polymers such as C₁₂KNC₁₂KNH₂ and C₁₂KKNC₁₂KNH₂ was reduced only by 2-folds after 6 hours exposure to plasma enzymes while longer polymers such as K(NC₁₂K)₃NH₂ and C₁₂K(NC₈K)₅NH₂ did not display any degree of inactivation even after 18 hours incubation.

Hemolysis Assays:

The toxic hemolytic effect of the polymers of the present invention on human erythrocytes (red blood cells, RBC) was assayed as described hereinabove. The results are presented in Table 3, under the column headed “LC₅₀”, in terms of the lytic concentrations that induced 50% (LC₅₀) lysis of red blood cells in phosphate buffer (PBS).

As shown in Table 3, polymers such as C₁₂K(NC₈K)₇NH₂, C₈(KNC₁₂K)₂NH₂, C₈K(KNC₁₂K)₂NH₂, NC₁₂K(KNC₁₂K)₂NH₂, C₁₂K(NC₈K)₅NH₂, C₁₂K(NC₈K)₆NH₂, NC₁₂(KNC₁₂K)₂NH₂, C₁₂KK(NC₈K)₄NH₂ and K(NC₁₂K)₃NH₂ (see, respective entries 45, 76, 77, 83, 43, 44, 82, 53 and 60 in Table 3) which exhibited high antimicrobial activity, displayed low hemolytic activity. As is further shown in Table 3, polymers including various fatty acid moieties conjugated to the N-terminus thereof and/or a relatively large number of lysine residues, were particularly found to exhibit potent antibacterial activity along with low hemolytic activity. These results clearly demonstrate the low toxicity of the polymers of the present invention against human red blood cells.

FIG. 6 presents comparative plots demonstrating the hemolytic effect of C₁₂K(NC₈K)₇NH₂, an exemplary polymer as presented herein, as compared to the hemolytic effect of bivalirudin, a synthetic 20 amino acid peptide, which is clinically used as a specific and reversible direct thrombin inhibitor approved by FDA for intravenous administration, and to the hemolytic effect of MSI-78, a magainin derivative that was recently assessed in human clinical trials for treatment of diabetic foot ulcers, determined against human RBC (10% hematocrit) after 1 hour incubation at 37° C. in presence of three polymer/peptide concentrations, namely 31 μM (striped bars), 94 μM (gray bars) and 156 μM (white bars). Plotted values represent the mean±standard deviations obtained from at least four independent experiments.

As can be seen in FIG. 6, C₁₂K(NC₈K)₇NH₂ did not exhibited any hemolytic activity when tested against human red blood cells at all three experimental concentrations, and did not yield the characteristic dose-response profile observed with conventional AMPs. Both bivalirudin, a non-antimicrobial peptide, and C₁₂K(NC₈K)₇NH₂ displayed merely a “background level” activity at least up to 156 μM, a concentration that corresponds to about 100 folds the MIC value of C₁₂K(NC₈K)₇NH₂ against various bacteria. Contrarily, MSI-78 exhibited a high degree of hemolysis at concentrations as low as 31 μM and 94 μM. Circular dichroism (CD):

The secondary structure of selected polymers according to the present inventions was studied by circular dichroism (CD) measurements in various media, as described hereinabove in the Experimental Methods section. The CD profiles of C₁₂K(NC₈K)₅NH₂ and C₁₂K(NC₈K)₇NH₂, exemplary antimicrobial polymers according to the present invention, and NC₁₂K₄S4₍₁₋₁₄₎, an exemplary dermaseptin derivative, are presented in FIGS. 7 and 8. The CD data presented represent an average of three separate recordings values.

FIG. 8 presents the circular dichroism spectra of C₁₂K(NC₈K)₇NH₂, an exemplary polymer as presented herein (gray lines), and control antimicrobial peptide K₄S₄(1-16) (black lines), taken in PBS alone (dashed lines) or in presence of 2 mM POPC:POPG (3:1) liposomes suspended in PBS (solid lines) (data represent average values from three separate recordings).

As is shown in FIG. 7 and FIG. 8, the CD spectra of the polymers of the present invention displayed a minimum near 200 nm, indicating a random structure. The same CD spectra were observed in assays conducted in the presence and absence of liposomes. The CD spectra of the control dermaseptin NC₁₂K₄S4₍₁₋₁₄₎ and control antimicrobial peptide K₄S₄(1-16) showed a typical spectrum characteristic of an alpha-helical secondary structure. Similar results were observed in 20% trifluoroethanol/water (data not shown). In general, secondary structure imparts a distinct CD to their respective molecules. Therefore, the alpha helix and beta sheet typically observed in polypeptides and proteins have CD spectral signatures representative of their structures. The lack of these characteristic CD spectral signatures representative of a secondary structure elements in the spectra obtain for the polymers presented herein is indicative of their “random” secondary structure, or lack thereof.

Surface Plasmon Resonance Assay:

The binding properties of exemplary polymers according to the present invention to membranes were studied using surface plasmon resonance (SPR) measurements, as described hereinabove in the Methods section.

The obtained data indicated that the polymers according to the present invention display high affinity binding to a model membrane mimicking the bacterial plasma membrane, with K_(app) ranging from 10⁴ to 10⁷ M⁻¹). FIG. 9, for example, presents the data obtained with C₁₂K(NC₈K)₅NH₂, and demonstrates the high affinity binding of this exemplary polymer according to the present invention (K_(app) of 9.96×10⁴ M⁻¹ to a model membrane.

An additional exemplary antimicrobial polymer according to the present invention, K(NC₁₂K)₃NH₂, displayed an even higher affinity binding (K_(app) of 6.3×10⁵ M⁻¹, data not shown).

These results substantiate the affinity of the polymers of the present invention towards the membranes of a pathogenic microorganism.

Lipopolysaccharide Binding Assay:

The binding affinity of the positively charged polymers according to the present invention to the negatively charged lipopolysaccharides (LPS) present on the membrane of gram-negative bacteria was measured as described in the Methods section hereinabove. The maximal binding levels of seven exemplary polymers according to the present invention, KNC₈KNH₂, K(NC₈K)₂NH₂, K(NC₈K)₃NH₂, K(NC₈K)₆NH₂, KNC₁₂KNH₂, K(NC₁₂K)₂NH₂ and K(NC₁₂K)₃NH₂, to liposomal membranes before and after incubation with LPS, as measured in these assays, are presented in FIG. 10.

As can be seen in FIG. 10, the binding affinity of a polymer to the membrane is affected by the length of the polymer. Thus, for example, the binding affinity of K(NC₈K)₆NH₂ is higher than that of KNC₈KNH₂ and the binding affinity of K(NC₁₂K)₃NH₂ was found higher than that of KNC₁₂KNH₂.

As can be further seen in FIG. 10, the same correlation between the polymer length and its binding affinity to LPS was observed. Thus, for example, the polymers K(NC₈K)₆NH₂ and K(NC₁₂K)₃NH₂ each exhibits close to 2-fold reduction of affinity to liposomal membrane following incubation with LPS, indicating binding of the polymers to LPS during the incubation period, which interferes with their binding to the membranal liposomes.

These results provide further support to a mechanism of action of the polymers that involves strong interaction with LPS, which promotes a destructive action against the bacterial membrane and by which the risk of development of endotoxemia is reduced.

DNA Binding Assay:

The binding properties of exemplary polymers according to the present invention to nucleic acids were studied by determining their ability to retard migration of DNA plasmids during gel electrophoresis in a 1% agarose gel. The obtained results show that the polymers according to the present invention retard the migration of various plasmids (e.g., pUC19, pGL3 Luciferase Reporter Vector (Promega)) in a dose dependent manner. Representative results, obtained with the plasmid pUC19 in the absence and presence of three exemplary polymers of the present invention, C₁₂KKNC₁₂KNH₂, K(NC₄K)₇NH₂ and C₁₂K(NC₈K)₅NH₂, are presented in FIG. 11 (Note: isolation of the plasmid from a bacterial culture results in three major bands and several minor bands, as seen in the leftmost slot of the gel's UV image). An apparent dose-dependent behavior was evident in the presence of the shortest tested polymer C₁₂KKNC₁₂KNH₂. The dose-dependent behavior was further accentuated with the longer tested polymers K(NC₄K)₇NH₂ and C₁₂K(NC₈K)₅NH₂. Thus, at the lowest dose of C₁₂KKNC₁₂KNH₂ (polymer to DNA ratio of 1:1), the supercoiled plasmid DNA band disappeared whereas the other bands displayed a smeared pattern. These results suggest that the inhibitory effect of the polymers of the present invention is higher with supercoiled DNA. Increasing the polymer doses resulted in accentuated effect, such that the retardation effect extended to all DNA species.

Furthermore, it was found that various polymer-DNA complexes remained intact after exposure to either DNAse digestive enzymes or peptidase digestive enzymes. These findings reveal a tight binding between the polymers of the present invention and the DNA molecule, exhibited by the mutual shielding exerted by the polymers to the DNA molecules and vice versa.

Saliva Microbicidal Assays:

The antimicrobial activity of an exemplary polymer of the present invention, C₈K₈, against microorganisms in human saliva was studied as described above. FIG. 12 presents the results obtained in this study in terms of the logarithmic units of CFU per ml as a function of the incubation time of the samples with the vehicle buffer (control), 113-367 (antimicrobial agent with known activity control) and C₈K₈. The results show that while in the control, untreated group the saliva microorganisms are persistent and proliferate without any treatment, the growth of saliva microorganisms treated is inhibited but proliferation is resumed after 30 minutes; whereby the growth of the saliva microorganisms treated with the polymer according to the present invention is inhibited without recovery.

Anti-Malarial Assays:

A of a group of polymers, according to the present invention, were tested for their anti-malarial effect on parasite growth and on mammalian cells. The obtained results are presented in Table 7 below, wherein:

“IC50 parasite (μM)” represents the concentration of the tested polymer in μM that is required for 50% inhibition of the growth of the malaria causing parasites, measured as described hereinabove (column 3 in Table 7);

“IC50 MDCK (μM)” represents the concentration of the tested polymer in μM that is required for 50% inhibition of growth of MDCK cells, measured as described hereinabove (column 3 in Table 7); and

“IC50 Ratio” represents the ratio of IC50 MDCK over IC50 parasite, indicating the specificity of the polymer to parasitic membranes over that of mammalian cells.

TABLE 7 Entry (entry in Table 3 IC₅₀ parasite IC₅₀ MDCK above) Polymer (μM) (μM) IC₅₀ Ratio A (54) C₁₂KNC₁₂KNH₂ 3.54 156.8 44.29 B (65) (NC₁₂K)₂NH₂ 4.63 609.2 131.58 C (55) C₁₂K(NC₁₂K)₂NH₂ 0.85 92.1 108.35 D (66) (NC₁₂K)₃NH₂ 0.14 48.3 352.55 E (56) C₁₂K(NC₁₂K)₃NH₂ 0.08 37.3 449.40 F (67) (NC₁₂K)₄NH₂ 1.59 57.0 35.85 G (58) KNC₁₂KNH₂ 68.20 693.8 10.17 H (59) K(NC₁₂K)₂NH₂ 7.85 157.4 20.05 I (60) K(NC₁₂K)₃NH₂ 1.72 347.0 201.74

As shown in Table 7, some of the polymers have shown very high activity against malarial parasites having an IC₅₀ in the sub-micromolar range, as presented in the column denoted IC₅₀ parasite (μM) (see entries D and E in Table 7 above). The structure-activity relationship conclusion that emerges from this series is that lengthening of the chain increases the anti-malarial activity (reduces the IC₅₀). The presence of the alkyl moiety at the N-terminus of the lysine, invariably increases the anti-malarial activity (see, entries G and A, entries H and C and entries I and E in Table 7 above). For some polymers, the amino alkyl adds further activity (see, entries C and D in Table 7 above) but this performance is not always consistent (see, entries A and B and entries E and F in Table 7 above).

There are similar consistencies for the effect of the polymers of the present invention on the MDCK cells. Addition of an alkyl at the N-terminus of the lysine results in a decrease in activity (see, entries G and A, entries H and C, and entries I and E in Table 7 above). The amino alkyl moiety usually results in decreased activity (see, entries A and B, and entries C and D in Table 7 above), but the opposite effect was observed for the longest polymers (see, entries E and F in Table 7 above).

The ratio of IC₅₀ is essentially equivalent to the therapeutic ratio. Thus, entries D and E in Table 7 above show the most therapeutically efficient polymers, according to the present invention.

Similar results were obtained with the primary cultures of cardio-fibroblasts (CF) and HepG2 transformed cells (results not shown).

Another series of polymers was tested for anti-malarial activity in order to further investigate the structure-activity relationship with respect to polymer length and hydrophobic moiety residue length.

The results, presented in Table 8 below, wherein “IC50 (μM)” represents the concentration of the tested polymer in μM that is required for 50% inhibition of the growth of the malaria causing parasites, measured as described hereinabove (column 3 in Table 8), indicate that the addition of caprylic acid (C₈) to the N-terminus of the lysine residue increases the anti-malarial potency considerably (up to 67 fold), but this amplification diminishes as the chain length increases. Substitution of C₈ with lauric acid (C₁₂) results in a further increase the anti-malarial potency (up to 20-fold), whereas further substitution at this terminus with ω-aminolauric acid (NC₁₂) reverts the potency considerably.

Among the most active polymers in the C₁₂K(NC₈K)_(n)NH₂ group, the anti-malarial potency diminishes with increase polymer length (see, entries 15-21 in Table 8 below). The opposite trend was observed for the non-acylated (at the N-terminus) group K(NC₈K)_(n)NH₂ (see, entries 1-7 in Table 8 below) although they exhibit an overall lower activity. No such consistent trends could be observed for the other groups.

None of the polymers of this series caused lysis of infected RBC at concentrations that are at least 2-fold higher than their respective IC₅₀ (data not shown).

TABLE 8 Entry (entry in Table 3 above) Polymer IC₅₀ (μM)  1 (32) KNC₈KNH₂ 260  2 (33) K(NC₈K)₂NH₂ 180  3 (34) K(NC₈K)₃NH₂ 130  4 (35) K(NC₈K)₄NH₂ 90  5 (36) K(NC₈K)₅NH₂ 84  6 (37) K(NC₈K)₆NH₂ 71  7 (38) K(NC₈K)₇NH₂ 47  8 (25) C₈KNC₈KNH₂ 16  9 (26) C₈K(NC₈K)₂NH₂ 2.7 10 (27) C₈K(NC₈K)₃NH₂ 14.8 11 (28) C₈K(NC₈K)₄NH₂ 48.9 12 (29) C₈K(NC₈K)₅NH₂ 44.1 13 (30) C₈K(NC₈K)₆NH₂ 30.5 14 (31) C₈K(NC₈K)₇NH₂ 37.2 15 (39) C₁₂KNC₈KNH₂ 0.38 16 (40) C₁₂K(NC₈K)₂NH₂ 0.2 17 (41) C₁₂K(NC₈K)₃NH₂ 1.16 18 (42) C₁₂K(NC₈K)₄NH₂ 2.43 19 (43) C₁₂K(NC₈K)₅NH₂ 5.57 20 (44) C₁₂K(NC₈K)₆NH₂ 9.9 21 (45) C₁₂(NC₈K)₇NH₂ 15.8 22 (46) NC₁₂KNC₈KNH₂ 120.1 23 (47) NC₁₂K(NC₈K)₂NH₂ 99.5 24 (48) NC₁₂K(NC₈K)₃NH₂ 93.7 25 (49) NC₁₂K(NC₈K)₄NH₂ 72.9 26 (50) NC₁₂K(NC₈K)₅NH₂ 70.6 27 (51) NC₁₂K(NC₈K)₆NH₂ 66.5 28 (52) NC₁₂K(NC₈K)₇NH₂ 89.8

The anti-malarial effect of the polymer C₁₂K(NC₁₂K)₃NH₂ (see, entry E in Table 7 above) has been tested by exposing parasite cultures at the ring and the trophozoite stages for various lengths of time and different polymer concentrations, the polymer has then been removed and after 48 hours all cultures that were subjected for the different treatments were tested for parasite viability using the hypoxanthine incorporation test.

The IC₅₀ for each treatment has been calculated for the chloroquine-resistant FCR3 strain versus chloroquine-sensitive NF54 strain, and the results are presented in FIG. 13. As seen in FIG. 13 the ring stage is more sensitive to the polymer than the trophozoite stage where it also takes a longer time to exert the inhibitory action. It also seems that the effect is cumulative in that the IC₅₀ values at 48 hours are lower than those observed with shorter exposure times.

The effect of time of exposure of parasite cultures to C₁₂KNC₈KNH₂ (see, entry 15 in Table 8 above) at different stages on parasite viability is shown in FIG. 14. As can be seen in FIG. 14, the results indicate that ring and trophozoite stages are almost equally sensitive to C₁₂KNC₈KNH₂, yet a period of 24 hours is required in order to exert the full inhibitory activity on the rings and more so for the trophozoites stage.

In-Vivo Therapeutic Efficacy:

The therapeutic efficacy of C₁₂K(NC₈K)₇NH₂ was assessed using a murine peritonitis-sepsis model after intraperitoneal infection with E. coli and intraperitoneal treatment with the tested and control agents one hour post-infection.

FIGS. 15 a-b present the rate of survival, monitored over a time period of 7 days, of infected mice (n=10 per group) inoculated intraperitoneally with 2.5×10⁶ CFUs of E. coli CI-3504 (FIG. 15 a) and 5×10⁶ CFUs of E. coli CI-3504 (FIG. 15 b), and subsequently treated one hour after infection by intraperitoneal administration of PBS (black circles), a single dose of 4 mg/kg C₁₂K(NC₈K)₇NH₂ (gray squares) or four doses of 2 mg/kg imipenem at (asterisk).

As can be seen in FIGS. 15 a-b, the polymer C₁₂K(NC₈K)₇NH₂ significantly prevented mortality of mice infected with two different lethal inocula. In these representative experiments, at the low dose inoculum (2.5×10⁶ CFU/mouse), survival of infected mice treated with polymer was 100% compared to 20% in the vehicle treated control group (p<0.005). At the higher dose inoculum (5×10⁶ CFU/mouse), survival was 80%, compared to 0% survival in the vehicle-treated group (p<0.005). Treatment with a classical antibiotic (imipenem, 4 doses during 28 hours, starting one hour after infection) resulted in survival of 100% and 90% in the two inocula studied, respectively. Overall, these results clearly demonstrate the beneficial therapeutic potential use of the polymers presented herein, and their efficacy in the treatment of harsh bacterial infections.

The results obtained in this study, which reflect a comprehensive efficacy profile, demonstrate that C₁₂K(NC₈K)₇NH₂, a polymer according to the present invention, although displaying less efficacious MIC levels (MIC E. coli of 3.1) as compared to certain classical antibiotic agents, such as imipenen (MIC E. coli of 0.6), the polymer still proves a more efficacious antimicrobial agent.

In-Vivo Toxicity:

In-vivo acute toxicity of the polymers presented herein was examined by intraperitoneal injection of 0 μg (blank control), 100 μg, 250 μg, and 500 μg of freshly prepared C₁₂K(NC₈K)₇NH₂, an exemplary polymer according to the present invention, to groups of 12 mice; thus the dosage corresponding to 0, 4, 10, and 20 mg/kg of body weight. Animals were directly inspected for adverse effects for 4 hour, and mortality was monitored for 7 days thereafter.

FIG. 16 presents the rate of survival, monitored over time period of 6 days, of female ICR mice (n=12 per group) treated intraperitoneally with 0 mg/kg of body weight (white bars) 4 mg/kg of body weight (sparsely striped bars), 10 mg/kg of body weight (densely striped bars) and 20 mg/kg of body weight (black bars) of C₁₂K(NC₈K)₇NH₂.

As can be seen in FIG. 16, only 25% of the mice treated with the highest dose of 20 mg/kg of body weight died, while all the mice treated with 4 and 10 mg/kg of body weight survived throughout the duration of the experiment.

Based on the experimental results presented herein, the polymers according to the present invention offer several advantages over conventional AMPs, which are mostly of limited utility as therapeutic agents due to their low bioavailability and/or high toxicity. From pharmacologic, therapeutic and other practical points of view, the polymers presented herein represent a novel and promising family of antimicrobial agents that are devoid of AMPs intrinsic disadvantages. They may therefore be beneficially utilized in various antimicrobial fields including the treatment of medical conditions associated with pathogenic microorganisms.

Moreover, the inherently simple and incremental nature in designing polymer libraries provides a new alternative and a systematic tool for the dissection of the relative importance of charge and hydrophobicity, the parameters believed to be most crucial to antimicrobial activity and their role in selective activity.

The peptide-like backbone, the physico-chemical characteristics, the broad antibacterial activity spectrum, the rapid bactericidal kinetics and the bacterial challenge in developing resistance, demonstrated herein for the polymers of the present invention, are comparable and even superior to those of conventional AMPs and thus reminiscent of their postulated membrane disruptive properties and other eventual targets. In this respect, the results presented herein may suggest that a defined secondary structure does not necessarily play a determining role. Rather, activity appears to depend substantially on a subtle interplay between positive charge and hydrophobicity.

It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination.

Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.

All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention. 

1. A polymer comprising a plurality of positively charged amino acid residues and at least one hydrophobic moiety residue, wherein at least one of said at least one hydrophobic moiety residue is being covalently linked to at least two amino acid residues in said plurality of amino acid residues via the N-alpha of one amino acid residue and via the C-alpha of the other amino acid residue in said at least two amino acid residues.
 2. The polymer of claim 1, wherein said plurality of amino acid residues comprises from 2 to 50 amino acid residues.
 3. The polymer of claim 2, wherein said plurality of amino acid residues substantially consists of positively charged amino acid residues.
 4. The polymer of claim 3, wherein said positively charged amino acid residues are selected from the group consisting of lysine residues, histidine residues, ornithine residues, arginine residues and combinations thereof.
 5. The polymer of claim 3, said positively charged amino acid residues are lysine residues.
 6. The polymer of claim 1, wherein said at least one hydrophobic moiety has a carboxylic group at one end thereof and an amine group at the other end thereof.
 7. The polymer of claim 6, wherein said at least one hydrophobic moiety residue is linked to each of said at least two amino acid residues via a peptide bond.
 8. The polymer of claim 1, comprising from 1 to 50 hydrophobic moiety residues.
 9. The polymer of claim 1, wherein said at least one hydrophobic moiety residue comprises a fatty acid residue.
 10. The polymer of claim 1, wherein each of said at least one hydrophobic moiety is an ω-amino-fatty acid residue.
 11. The polymer of claim 10, wherein said hydrophobic moiety is selected from the group consisting of 4-amino-butyric acid, 8-amino-caprylic acid and 12-amino-lauric acid.
 12. The polymer of claim 1, comprising at least two hydrophobic moiety residues, wherein at least one of said at least two hydrophobic moiety residues is being linked to the N-alpha of an amino acid residue at the N-terminus of said plurality of amino acid residues.
 13. The polymer of claim 5, comprising 2 to 50 lysine residues and 1 to 50 ω-amino-fatty acid residues, wherein: at least one of said ω-amino-fatty acid residues is covalently linked to at least two of said lysine residues via the N-alpha of one lysine residue and via the C-alpha of the other lysine residue in said at least two lysine residues, said at least one ω-amino-fatty acid is linked to each of said lysine residues via a peptide bond, and wherein: each of said lysine residues is independently selected from the group consisting of a lysine residue and a lysine residue having a fatty acid residue linked to a side-chain thereof; an N-terminus of the polymer is selected from the group consisting of a lysine residue, an ω-amino-fatty acid residue linked via a peptide bond to a lysine residue and a fatty acid residue linked via a peptide bond to said lysine residue; and a C-terminus of the polymer is selected from the group consisting of a lysine residue and a lysine residue terminated with an amide group.
 14. The polymer of claim 13, wherein said ω-amino-fatty acid residue is selected from the group consisting of 4-amino-butyric acid residue, 6-amino-caproic acid residue, 8-amino-caprylic acid residue, 10-amino-capric acid residue, 12-amino-lauric acid residue, 14-amino-myristic acid residue, 16-amino-palmitic acid residue, 16-amino-palmitoleic acid residue, 18-amino-stearic acid residue, 18-amino-oleic acid residue, 18-amino-linoleic acid residue, 18-amino-linolenic acid residue and 20-amino-arachidonic acid residue.
 15. The polymer of claim 14, having an amino acid sequence selected from the group consisting of the amino acid sequences as set forth in SEQ ID NOs: 1-83 and 86-94 as set forth herein.
 16. The polymer of claim 15, each of said w-amino-fatty acid residues covalently linked to said at least two of said lysine residues is 8-amino-caprylic acid residue.
 17. The polymer of claim 1, further comprising at least one active agent attached thereto.
 18. The polymer of claim 17, being capable of delivering at least one active agent to at least a portion of the cells of a pathogenic microorganism.
 19. The polymer of claim 1, being selected from the group of compounds presented in Table
 3. 20. A pharmaceutical composition comprising, as an active ingredient, the polymer of claim 1 and a pharmaceutically acceptable carrier.
 21. The pharmaceutical composition of claim 20, further comprising at least one additional therapeutically active agent.
 22. The pharmaceutical composition of claim 21, wherein said at least one additional therapeutically active agent comprises an antibiotic agent.
 23. A medical device comprising the polymer of claim 1 and a delivery system configured for delivering said polymer to a bodily site of a subject.
 24. A food preservative comprising an effective amount of the polymer of claim
 1. 25. An imaging probe for detecting a pathogenic microorganism, the imaging probe comprising the polymer of claim 1, said polymer further comprising at least one labeling agent attached thereto. 